Assalamualaikum
This is entirely my opinion, but I want to mention it anyway.
I dont think that the size of the garment matters. I mean when we shower, we are obviously not entirely covered, yet we perform Wudhu, or during Ghusl. We do not bathe with our clothes on, well not so wrapped (if I can say) at least. Like Sister ShyHijabi said, what matters is that the water gets to where it should and the parts prescribed are cleansed thoroughly. Some people find it easier to perform Wudhu without clothes on. I dont mean entirely unclothed, I mean example, some may perform their Wudhu (not including Istinja) in a bath tub, so a shower basically without washing hair. So yeah, I guess it doesnt really matter. The Brothers are going to get you a fatwa anyway.
Assalamualaikum