well you could have it so they can’t be anchored within 100km of each other, then just make their ranged shorter than 100km, this way each one acts as its own sort of missile spewing defensive bubble, this way it its field of fire or area coverage would be lower than that, so you don’t over lap the fields of fire but they do encroach onto the grid where battle is being planned
port the structure rules into this deployable so you can’t spam them around gates, asteroid belts and such things and it becomes a bit more strategic, at least thats what I would do
pulling a number out of the air, 100km anchored appart
50km range
S = Structure
O = Flak platforms
O --------- O
S
O --------- O
in this example you’d have to consider them to be at the appropriate spacing appart and assuming 100km from the structure also
you could theoretically create a sphere of them, however they’ll poof out after a couple of hours, meaning that they’ll either act as a deterrent OR if the attacking fleet warps to grid, depending on the angle of entry one of the batteries will open up.
in this case this its basically access control for a small area for an independant spot on grid, where you just need to hold up for a couple of hours, it’ll give some defensive capability
alternatively these could be used as some form of decoys, basic defense batteries to entertain your unwanted guests when they enter system, give them something to pew a little bit.
—edit—
the flak platforms in the image above are not representative of their range, simply a location of the physical asset