The supports/props need to support the weight of the bunch at the very highest point. They should be at a point where they would actually support the bunch is you cut the stem. In a manner of speaking, you are hanging up the entire plant and the bunch, as if you had cut the plant off the ground, and hung the whole thing, bunch and all, on a hook. The purpose of supports/props is to take the weight off of the pseudostem so that it doesn't bend/fold/break.
