Im not expert and im just making an assumption here, but I'd assume that It does not effect the sensitivity per-se... however it may effect the interpretation.
In non-pop mode, the detector may not be optimized to detect very short ka bursts. It either ignores them (as falses) or it misses them on its scans.
In pop mode, these shorter KA burts are either not missed or not ignored... hence the higher odds of falsing. I'm not sure there is any effect on the ability of the detector to sense a "weak" signal... only a "short" one.