I had a brief outline for an idea to scale the EHP of any structure against the size of the fleet. People have suggested such things as scaling resistances, or 10-min RF modes when under high DPS, but I never really liked them so much.
How about the sig of the structure reduces as more red-box locks are made upon it. Passive and repping locks therefore wouldn't count. I'm sure some sort of sliding scale could be used such that larger forces give diminishing returns.
The benefit of this approach is that although you obviously want to minmax the pilot:dps ratio, at some point the smaller sig resolution of smaller guns comes into play and it's suddenly better to have Cruisers at 4-500 dps rather than Battleshrimps at 7-800 dps because of the actual damage being applied. So although the EHP of the structure never actually changes, it is protected from overwhelming force due to increasingly diminishing returns.
Might have to give these structures painter immunity to avoid making painters mandatory fittings to circumvent the mechanic.
RP justification: Some sort of technology only equipped by certain structures. Or a special kind of weapons interference that applies due to special armor plating. Or something else.