Well yeah, but if your avatar is anything to go by, you’re a kiwi. Every vowel is a schwa for you. 
What do you mean all vowels aren’t in the middle of the mouth??
yeah it does tend to confuse things. My parents must have had some foresight though, to put me into speech lessons as a child. So maybe I’m a little less disadvantaged than the average kiwi.
I also think so, but TBF, the diphtong is super weak (or practically nonexistant), so it sounds more like ‘hee’ usually (at least in a compound). However, I don’t know if that relates to what @Kjwoods is saying 
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That sounds like it would be missing the ‘h’ at the beginning to me.
Thanks @morteasd you’ve hit the nail on the head and said it much better than me. Pronouncing it as “hey” didn’t come out right because as you said the second vowel is very light. I agree, more like へ+え sound.
And yes should have been “hairy” without the R, my mistake.
Do you also experience the same thing with all ei sounds? Like べい for example? The mnemonic for this was Bay and I also had to self correct.
I guess this will be less of an issue once I’m doing a lot more listening and not just WK / reading, but I’d really like to avoid cementing incorrect pronunciation in the meantime 
Hmm, I think I stopped using them quite early on, or made my own. I had a pretty strong base of Japanese pronunciation, so it annoyed me more than confused. Since the ‘i’-vowel is still written there, it wasn’t that big of a stretch.
Biggest thing that actually confused me was mixing the こく and かく readings (and I still sometimes do).