The unlevel ground shown here is exaggerated for illustration. Up to some mechanical limit, the actuated "toes" on the foot will calibrate themselves to the ground continuously. Flexing back and forth seeking equilibrium from the sensors. I'ld picture the central ankle/foot portion to be kept horizontal by the passive linkage with the body through the 4 bar linkages and the outriggers. The toe actuators are levered from this central foot "stage". Toes activate proportionally to pressure sensed.