I'm sure that could have been a reason that Nasu might have made up at some point in the original NSFW Fate series works to support possible mana transfers. An unusual but simple: 'we might as well be naked, so it's more efficient when you need to top up on mana.'
hyooah!?Sup, Osakabehime.I've finally made it here.This body is an alter ego divine vessel made with lotion.It wasn't my intention to appear fully nude.Normally, I wouldn't show so much skin in front of a woman.I just didn't have enough magic power to create clothing.To begin with, forming clothes is quite the difficult thing to do.It may as well be impossible with how little magic power I have.Learning from this, I realize how amazing servants are for being able to keep their clothes on.It's given me great insight.My true body is still imprisoned by the demons in Chaldea.If you remain naked you can focus all your remaining magic power to battle.Servants will be at their best for battle if they are also naked.This makes Roland rational.Your excuse to justify being nude is too long...I apologize for looking immodest.
