I didn't mean to replace your mechanics with just shorter ranged weapons firing first. What I did mean is to use weapons, that are already assigned to some (choosen) fire control, in order of their max range ascending (the same way their targets are already ordered).
It will not change the option to diligently manually assign shorter ranged weapons to a separate FC with higher priorities (or other way around) and so make a leak even less probable just with a cost of more FCs to build and more micromanagenent to bring on. Yet it can make manual reassignments less tedios during battle and a rule "you need a separate FC for every max range of weapons or your PD will strangely leak" less suppressing.
If I read this correctly, it sounds like the concern is that the auto-assignment would assign a missile at a short range to the longer-range weapon, and then when the shorter-range weapon (assigned to the same BFC) looks for a target it might not be able to find one even though there are missiles at a longer range - which the longer-range weapon could have targeted.
So the suggestion is, for weapons assigned to the same BFC, that the shortest-range weapon (within a group of weapons at the same priority) should have target assigned first to prevent this possibility.
I think it is probably a rare edge case, both practically and because most people use dedicated BFCs per weapon type for point defense, but I can see how one might end up sing BFCs "suboptimally" in several cases (either roleplay or out of necessity) so it is probably worth the correction. Of course, weapons assigned to different BFCs would be handled as Steve already described.
@serger does this sound correct?