Normally with Khouri's Healing skill it should heal crusaders in the line in front of him by 30% of their max hp per second. However I noticed if you buy a crusader level it also activates his ability. Meaning that you can spam his heal more than once per second by constantly buying crusader levels, so you can tank hits until you either run out of gold or enemies deal enough damage to pretty much 1 hit kill your crusaders.