How to military press correctly. The secret is to use your whole body. Just like in the hollow position, you have to tuck your pelvis forward and squeeze your glutes hard. The harder you can squeeze, the more force you can use from the ground, through your statically flexed quads, through the glutes and up towards the upper body and the bar itself.
When your whole body is rock solid from flexing, no force dissipates and you are instantly stronger, without gaining an ounce of muscle.