Yes, I think you are right. I was thinking more in terms of how a kanji reads before modification.
How about this rule:
*), the first on-yomi ends in つ.* 吸血鬼 (きゅうけつき) is not affected, for example.
You can have gemination on items that don’t end in つ.
く is probably the second most common. (がく＋こう＝がっこう)
And there are other exceptions.
苦い（にがい）bitter
若い（わかい）young
My brain likes to say it knows these things and automatically gets my fingers to type them in and smash enter. Thanks, brain. 
苦い にがい
にくい
I used to mistake these two.
Pretty much just leeches left in my apprentice bucket:
Die, damn you!
As opposed to a rather rosey view in the late stages:
I’ve had troubles with the on’yomi readings of 楽, being either らく or がく
Then I accidentally noticed:
I am not sure this is a 100% rule, but I have looked at many examples so far and it always worked.
Anyway, it feels so good squashing that leech
FYI I wrote a script to help train on readings for leeches: [Unsupported] Leech training script.
札 (さつ）
礼（れい）
I always get these mixed up. A note though is made of paper (wood/tree) and thanks is made at an altar (pelican in WK).
I think it would help if WK had a list of words often confused, like English text books show words that are often misspelled or sound-a-likes. The part of WK that reinforces my leeches is using English pronunciations to approximate Japanese sounds. for example using May as mnemonic for まい causes me to get confused with めい due to the sound sound May makes in my head.
When I started WK, knowing 名 was part of 名前 messed me up because I kept reading it as まえ by mistake…and it sounding close enough to めい definitely didn’t help. If I make that mistake again when it comes time to burn, I swear I’ll scream.
I just had my mind blown:
I was getting so annoyed about あまりありません being difficult to read that I looked up if one of these words could be written in Kanji. Yep, あまり is 余り. “Huh thats odd- NO WAIT THATS 余る !!”
あまり comes from 余る 
And that’s how I remembered the reading of 余る forever and why I’ll never write 余り in Kana again.
Why why why can I not get 留学 right? I don’t understand. I know its study abroad. I say study abroad. I type exchange student. every. time.
Also, any kanji with the meaning of anticipation or expectation will not stick to my brain. Its maddening.
Any vocabulary that includes 近 kills me. Is it soon, or recent, or nearby?
I was very close to making that exact mistake in the last 15 minutes!
And I empathize re. 近 words. I’ve messed a lot of them too.
I need to exorcise 年中 i’d rather it not stay a leech year round plus it’s got that lovely rendaku going on
I’ve had 1000 reviews for about 6 months so I’m treating all my items as leeches.
My strategy is to write out lines of the ones I get wrong when doing reviews until I get a page of fails, to generally stay below 1000 review, and keeping on top of my current level and keep progressing… I always find items in higher levels that stick easier than others so I’m trying to speed along and then pick up the pieces later…
it’s not great but it’s working slowly
I got the meaning by using the rectangle in 中 and imagining myself walking around it and around and round and round, year round.
how come my leech number is over 200, 200 leeches ? feelsbadman…
After finding this topic I started tracking my leeches on my phone’s notepad feature in order to better remember them in the future. Then I realized a lot my leeches are a result of being unfamiliar with hiragana spelling conventions. In particular for me, I noticed I have terrible time remembering when to use a double UU or OU. It seems to me that the sound-alike mnemonics make it worse because I remember an English sound and spelling of the word. Any suggestions on how to deal with this would be appreciated.
I don’t know how much it’ll help, but I know I made those mistakes relatively frequently early on and they gradually started occurring less and less. Now I can’t remember the last time I’ve been unsure about the extra u. So hopefully the more exposure the more you’ll get used to it without having to do anything special.
