I do not understand the practical application of the din of being megale tefach or 2 in the bathroom. It does not seem possible with our modern day toilets to apply these shiurim. Perhaps in the old days when I guess they squatted over the ground, one could manage with only revealing a tefach or 2.
The main difference between our days and the times of Chazal is the different clothing we wear. In addition, the toilets are different. Therefore the shiurim of a tefach and two tefachim do not apply today (one would risk becoming dirty), and the principle is that one should try to act modestly even in the bathroom.
See Kaf Hachaim (3:12, quoting from Ben Ish Chai), who writes that when there is a risk of becoming dirty, one may be lenient in a walled bathroom.