I think the big problem is here: To activate a psychic shield you roll a psychic potential roll, not a psychic protection. To defense, after you have succeded the psychic potential roll, you use the psychic protection.
If you don't maintain the shield with an inniate slot, you must roll every round the psychic potential roll, like as you activate the shield every round.
Also: If you put the psychic shield into an inniate slot, it is possible that your shields starts to getting weaker.
For example: you have a psychic potential of 80 and activate a psychokinteic shield with an final roll of 141 (which would be Very difficult, therefore 700 LP). After this you but the shield into your inniate slot. Now, inniate slots only maintain powers on the level of your psychic potential or lower (which would be 80, also Medium, therefore only 300 LP). Because of this, your shield loses 5 LP per round up to the moment, on which it only has 300 LP, than it will only lose LP from attacks.
If you don't maintain the shield, every round a psychic potential roll is needed, therefore possible to get on round a stronger shield, the next round a weaker and another round no shield at all.