And my standard opfire filter is to set all ATGM to a number that's above the APCS and light tanks, so only MBT trip opfires. That is for MBT - where missiles are rather limited ammo items.
In WW2, I may do the same with heavy ATG or big gun tanks if I see a swarm of light tin cans coming my way, with big tanks lumbering along in the background. Let the 37mms (towed or on lesser tanks) deal with the tin-plated stuff.
In PBEM, you may find that a human opponent likes to recce with tin cans to draw fires. So perhaps, set a filter for your decent stuff to ignore them, maybe with one or 2 little 45mm guns set to close range fires in case an armoured car gets a wee bit closer than you would like. If he likes "recce with jeeps" - that is what your MMG sections are for..
The "interest circle" is rather good for focussing fires on things you may know are coming - say at a gap in the trees on your flank, or on the exit from a village. In this case your recce troops have seen suspicious activity, or you just have a hunch that a bunch of juicy targets will be appearing there
!.
Of course - if the opfire does not trip, and he leaves a vast herd of tin can armoured cars or (
especially) loaded APC out in full view in "shooting-range" conditions, by all means, blaze away when it is your turn
!