wheel & tire shops are going to suggest conservative & what they KNOW to fit, the last thing a tire or wheel place would want to do is try to push the limit & then wind up with a fitment problem, it would cost them $$$ cause if what they suggest don't fit then there going to have to eat it, so you are def not going to get anyone that will really spec something that they think there could be any chance of fitment issues. this does not mean that you can't go wider though, only that you had better be real sure because once you say "I want these, don't worry about weather you think they fit or not, I'll accept full responsibility" then your taking the risk, not them.
this is what I winded up having to do. when I ordered my 11" rear wheels from Iforged even they insisted that it will not fit. the only way I could get them to build the rim I wanted was I had to accept full responsibility for fitments, even had to sign a wavier from Iforged accepting the dimensions I ordered & that specifically stated that fitments was not guaranteed by them.
I wanted the same thing you want, I too am awd, so the first thing I winded up doing was a whole lot of research & measuring & spent a lot of effort trying to find the most extreme fitment I could. the easy way to do this is to just copy what's been done before & proven to work, but no one had anything like what I had in mind & everyone said it won't fit, so I was on my own & when I was as sure as I could be that I can get the wheels & tires I had in mind to fit I ordered them & then kept my fingers crossed for the next 2 months until I received the wheels & was able to test fit & they did indeed fit.
I haven't done much research on 20's because I already had 20's & I knew that I wanted 22's. I don't remember all the different options for tires I found that were possible candidates, all I remember is what I did wind up ordering, which is like I said before, 315/30-22's in the rear & 265/35-22's in the front. if you don't want to do all the research & figure out for yourself what will & won't work then you are welcome to just copy my setup, it is proven & it does fit & it is the most extreme fitment I've ever seen on a stock bodied fx too, AND it is also confirmed to work just fine with AWD. if you copy it then you would be taking advantage of all the research & risks that I have already done & taken with this, again it's either copy what's been done & proven or learn everything you'd need to know to make your own judgment.
heres a few shots of my fitment, first one shows the wheels tucking up into the well with no rubbing. I doubt you'll ever wind up as low as I am, at this much lowered ride height I did need to roll my inner lip, but before that with just a set of lowering springs I did not need to roll the lip at all & still had no contact, you'll only need to roll if you go much lower than stock & go even lower than just a set of lowering springs would give you. don't mean to spam your thread with my pictures but from what your saying it sounds like this is about what you are ultimately looking for.
