I was practicing this the other week and realized a few things that may be of use to you, please bare my rudimentary thoughts:
I find that if i am able to maintain perfect structural alignment, especially the core area (tail bone tucked up, abs contracted a little, and whilst in battle stance i have correct weight distribution), i can feel my lower back more
Send the awareness to the lower back and try to keep it there
I am very disconnected with my lower back, and find that i must do warm ups to help connect my mind to the lower back muscles. I notice that if i take a basketball and bounce it off a brick wall and then catch it, within the natural motion of catching the ball, my body already knows how to create the "spring load effect". The body, when catching the ball, automatically bends the needs, pushes out the lower back, sinks down and hollows the chest. Ahh! So it's this "catching the ball" posture that i'm looking for!
Maybe the Wing Chun masters knew about the "spring load effect" and had studied it extensively....is this why we are taught to be in almost the "catching the ball" position in our proper Wing Chun stance? When in this position we already are in position to absorb incoming shock, and am in position to release this latent energy outwards from the sprung position. This is genius thinking on the Master's part.
When i am in perfect structural alignment and palm strike upwards, by popping the hip flexer of my striking side, i automatically am able to create the spring load via the opposite side of my lower back. So for example if i am in battle stance, with left leg as lead and right as rear, and i strike upwards with the left hand, i am able to pop the left hip flexer up, as i visualize also elbowing someone behind with the right (Wu Sau?); as i do that, i notice that i automatically sink down a little with both legs (still maintaining 40 lead leg/ 60 rear leg), and as i do that my lower back pops out.
Have to be able to feel the kinetic chain; the striking hand and the guarding hand work together in opposite directions to create that snap, generating short form power; if the upper body is connected with the lower body (through perfect structural alignment), as i engage in the upper body "snap", automatically the lower body engages itself and creates a kinetic chain with the hip flexer on the striking side and the popping of the lower back on the opposite side (of the striking side).
Hope it helps!
▶️ 3Speak