Hi some of this can be guessed at and these are my thoughts. Firstly they would probably weaken and stop leaking if you used too much. A shroud is most likely a part of the safe mana calculation like other Attunement functions. The guardian Attunement as it gives a shroud right away probably attributes more mana to this early on. They probably do push more mana into the shroud as a part of their key attribute which is shroud manipulation. Mara makes hers larger at one point to be bigger than the school issued shield. Someone could I think use their shroud like Mizuchi if you read up on Edria attunements some imply they do just that.
Firstly they would probably weaken and stop leaking if you used too much. A shroud is most likely a part of the safe mana calculation like other Attunement functions. The guardian Attunement as it gives a shroud right away probably attributes more mana to this early on. They probably do push more mana into the shroud as a part of their key attribute which is shroud manipulation. Mara makes hers larger at one point to be bigger than the school issued shield.
Someone could I think use their shroud like Mizuchi if you read up on Edria attunements some imply they do just that.