These PIR sensors are not very directional, they look everywhere at once, so t
they aren't very useful for counting. The Prismatic polythene lens used provides
sensitivity to motion by fragmenting the heat image, so that motion leads to
intensity variation.
A thermal imager is needed for more localized sensing I reckon. You can get
4x4 thermal imagers, but they cost more and the lenses for them are expensive
too unless you can make your own from pure germanium or silicon or certain
plastics, or make do with the reduced sensitivity of a pinhole camera arrangement.