Red smoke on taget obscures F16 IR Maverick from locking(?)

[ACME_WIdgets]

In the F16, I can get a TPOD lock on a ground target with red identifying, smoke from 20+nm.  But once w/in 6nm I unlock/re-lock the TPOD and the IR Maverick most of time has difficulty in locking on.  I do see the hand off trying to take place. I'm typically 2-5k AGL, 300-400kts level, trying to get, unlock, get lock 3 times and it never locks. Not using TPOD gives same results.
Yes to: is hand off in Auto,  range 6-2nm, boresighted (looking at Mav display to make sure target is within center of crosshairs).

Targets w/out red smoke, same size, lock at 6-4nm range typically.
I find it easier to lock with CCD Mavs vs IR now a days.