Mechanics — how hard the balls are
1.0 is the stiffness that exactly sustains the requested
output — an overdamped ball moves at k × overlap, so the flux
P fixes a reference k. Below 1 the balls swallow
divisions by deforming: the tissue gets denser instead of moving, the
conveyor stalls, and the realised output falls short. Above 1 nothing can
compress, so every division shoves somebody and a fast divider
evicts itself. Compare realised output with the target.
The hierarchy
D = 0 is the flat crypt: no progenitors, the stem cells
do every division themselves. Watch the rate that demands of them.