As it stands from my experience with this skill is it only comes into affect when you are worldbound. This does not happen very often at hero levels because there are so few anti-paladins and even then its very hard for them to worldbind in the first place against the average paladins save vs spell. Since the faith virtue is already the most narrowly defined in terms of use perhaps it would be nice if silent prayer were able to help in the silent tower. Paladins more used to communing at a distance from their deity won't get hammered so hard on mana. Maybe make it just 1.5 times mana or what would be neat is if it was random between normal mana cost and double mana cost. This would allow just a little more utility to a very underused ability in a virtue that oftentimes cannot be used because of its narrow focus.