I’m also not sure how すっと would apply here based on the definitions from Goo.
Regarding the meaning, I also got the impression that Aika was commenting on Akari’s posture, but like you I’m not really sure how the text would mean that.
According to jisho, ごし is only used as a suffix, so it might not be that.
Maybe the third definition? Also in Jisho.
It seems unlikely to me that Aika is commenting on Akari’s posture because she’s not actually looking in her direction.
At first I thought it might be an idiom, but I can’t see anything on this list which matches (however if someone else would like to double check, that would be great!)
Now I’m wondering if it could be a phrase which means something like 落ち着いている - to make a contrast before the last few panels. Or even something in dialect equivalent to my butt has gone to sleep?
But I haven’t had any luck googling it. 
Usually after I read 2 or 3 times a chapter I double check with an english edition the panels that I’m less confident with… and this gem popped out:
Someone was not paying attention to their geography class.
Is that the official English version?? 
I don’t think it is, there are other panels with pretty bad font so I would assume this is a fan translation. Still hilarious
EDIT: checked and it’s a fan translation. That’s another proof that using fan translation to back up your study is never a good idea 
there are several occasions where the source I used is wrong and turns upside down the meaning of what is said in the original.
Agreed. I tried to look at a fan translation of ご注文はうさぎですか, but I quickly found out that it was unreliable.
Is that any good to read? (I mean as more japanese material)
It’s good for the most part, but much much more difficult than Aria. To read a chapter of Aria, it takes me 1-2 hours, looking up a handful of words and understanding 80-90% (possibly more if I dig a little bit into what I don’t know immediately). To read a chapter of ご注文はうさぎですか it takes me about 2 hours, looking up a ton of words and understanding 60-80% depending on the chapter. And those chapters are only 8 pages long.
Now, if you’re wondering if it’s good learning material (not just good entertainment) it depends on how well you retain words you’ve only seen once. For better or worse, most chapters follow a different random theme, so the vocabulary needed from one chapter to another changes significantly.
I did nominate it for the beginner book club, so feel free to read the sample pages and vote for it next time around if you’re interested.
I check against the English translation too, but I sometimes to it too soon, which colours my understanding of things. ADV’s translation says “Scottish Highlands”.
Perhaps. But also perhaps she’s demonstrating the required posture. Akari’s expression certainly makes it look like she’s being told off for something.
Hah, I had the same thought but came up similarly blank.
Maybe we need a native speaker. We could, hypothetically, tag someone with a Japanese girlfriend. 
Well, it could also be her “Aika is saying something weird” face too, like from page 103.
Maybe @Naphthalene would know, no native speaker necessary. 
Wha…? Someone called?
Sorry, I’m on a business trip, and it’s hard to keep up with the thread. (Also I don’t have the book with me).
Can someone post the page? (or pseudo-pm it to me I guess).
Page 147 (for others following along). We’re trying to figure out what the handwritten text in the first panel means. No worries if you don’t have spare time!
Ah ok, I thought it was 腰が入ってない in her accent (てない->ておらない->とらん)
(That expression means “you’re not doing any effort”, which is both in line with her personality and the fact they are in the middle of a training session) I guess there’s “you’re not putting your back into it” in English, but I may be misremembering.
That being said, it does look like a ス upon closer inspection, but then I don’t have the foggiest.
Now I’m looking closer at Aika’s hand on her chin, and that seems like a “hmm…” type of hand position, not something you’d do while criticizing someone. (But that’s my American interpretation of the hand gesture, I would have no idea if it means something different in Japan.) All I can say to that is hmm…
Oh no, maybe we do need a native to confirm!
Oh, gosh, this doesn’t sound promising I will probably try it, just for the kicks, but I don’t think I have the necessary vocabulary yet maybe in the future? I’ll give it a look!
Maybe we should write to Amano-sensei and ask.
Think ADV went with something like “keep your back straight”, though I don’t have it on me right now to check.
I feel like I could get to level 60 and learn several hundred new words and still have to look up a ton. It’s a comedy manga, so sometimes I understand all the words and (I think) all the grammar, but still don’t get the joke. It’s kind of annoying, but it’s still fun enough to keep reading. I’ll probably read the rest of volume 2 and then focus on something else that’s at a better difficulty for me. But I already have volumes 3-6, so I’ll go back to it at some point.
Well, the number of pages in this chapter with few or no words meant that it was easy for me to catch up after having a busy weekend at least. 
You are not making it easier 
Still, jokes are really hard to understand. It’s not even a matter of pop culture, they are just… hard, in all languages. The only harder things after jokes are idioms. I had to buy an idiom vocabulary to understand my colleagues when I moved to the UK 
Heh heh heh 
seriously though, I’m sorry - it’s so ingrained it doesn’t even register
I have a small grammar question / clarification request if anyone is able to help me out!
Page 118
Panel one from the top, left-hand speech bubble
In describing the cat, アリシア says 牡牛くらい大きい黒猫だそうよ. I’m guessing this means ‘a black cat about as big as a bull’? Is putting [noun くらい adjective] a particular grammatical construction?
And… I guess while I’m on this page 
in the bottom panel, right-hand speech bubble, she says 入れないらしいけど, which I assumes means that humans aren’t allowed in, but I don’t think I’ve come across that らしい ending before anyone able to illuminate me?
