Swimming in roomscale by swinging you hands activates even if a player is not fully in water. While being one block deep might be useful (short players for example), being half block deep just doesn't feel right. Imo solution is to make being half block deep in water not activate the swimming.

In videos below I'm playing standing on 101% player height.

One block deep:

Half block deep:

hm, yeah. I agree about the half block water, but full block should stay, since it's swim able in vanilla, also swimming in 1 meter deep water is not unusual