Well, one question now is whether there's still a need for the 25%-damage-output-when-under-an-ff rule. It's now much harder to indefinitely sustain the fortified position. On the other hand, it does definitely majorly increase the survivability of offensive turrets and you'd basically never want to _not_ put them under an ff if there's no such reduction.
Another thing would be to increase the range of the fighter and whatnot, but then it would just be a micro question of whether you actually kept them out from under the field, etc.
Id go for removing the 25%, especially with the FF nurfs and since from the sounds of it you will be nurfing the hardened shields anyways. In reality the penalty seems to be more of an annoyance than anything, if you are too concerned about the turrets living to long, then keep the damage penalty for the turrets, but everything else can shoot full strength.
Edit: bah responded with same idea as mindloss before i had read as far as his post, only I like the idea, dosnt feel hacky to me