18x8.5 ET45 isn't flush. It might look flush at stock height, but when it's lowered, isn't flush.
I've recommended many people with 18x8.5 ET35 with 235 Michelin tires, that are perfectly flush fitment. I'm currently running 245/35/19 on 19x9 ET45. I'm planning on putting 3mm front and 5mm rear spacers to push them out. I don't rub fender with my setup. I'm rubbing fender liner when doing 95mph plus hitting a big freeway dip. My favorite wheel fitment is 19x9 ET42 with 245 or 255's.
18x9 ET38-42 with 245/255 tires should be solid. From the photos of your car, you aren't that low. I'd assume given that same height, you shouldn't have any issues with 245 or 255's.
Remember 255/35/18 has same sidewall as a 225/40/18. 245/40/18 is quite a bit more sidewall than 255/35/18.
You can check out my fitment guide on my page -
https://www.big-euro.com/mk8-gti