The gap between surfaces, not the body size, switches fusion in a pattern-forming chemical medium

A reaction-diffusion medium with an uneven, striped supply is used to ask what decides whether two blobs of pattern fuse into one. Enumerating all positions modulo the stripe period gives 144 phase classes and nine distinct local supplies. At a fixed supply the bridge of chemical between the bodies decides the outcome (logistic slope 6.09, z 5.8 at radius 6; 4.85, z 2.7 at radius 3), with the supply-fusion association carrying the opposite sign at the smaller body. The surface-to-surface gap switches fusion (share 0.00 at a 12-cell gap, 0.19 at 10, 0.40 at 9, 0.83 and 0.96 at 8) while the body size shifts it by about a tenth. Replacing runs by worlds leaves an AUC at 0.652 to 0.660 but moves a deviance drop from 20.7 to 14.3, inside that test's own bar of 20, so the unit of observation has to be checked per statistic.