2 things to be careful of (and the calculations are not understood by me yet so I can't advise)...
You don't want the tire out so far that your quarter panel lip cuts into the sidewall and not in so far that it hits the suspension.
I think some are hesitant to give you the thumbs up on a particular size because in the end it's your responsibility.
I do know that Works will tell you the proper size range if you contact them directly. However... Seeing it and how the exact fitment is, is not always exactly what you expect . I think that's why this area has sizes and fitment... Lots to read....
Some people can go in farther on the rears if they are stretching the rubber so the tire size plays in to it as well.
As a note, I am considering going to 16's because I wont be running a BBK and I really notice the thin sidewall on my 18's when it comes to traction now that my car is a BPU Supra. On stock suspension and stock 7MGTE setup it wasn't so bad, but I break traction in second gear and sometimes in third gear as well if I shift too quickly which gives my Supra a bit of a tail wag... the 16's with a wider sidewall might allow for a better pull I think.