it seems to me that this is one of those approaches that is always going to be difficult if you are accustomed to the low angle "drag it in on the back of the drag curve" approach that I so often see. In those situations you are closer to the ground (and used to seeing the ground close to you) and you are then juggling the throttle to adjust the vertical speed to keep the runway in view. You can easily end up lower than the runway (but with it still in view) without realising it and a massive increase in power is required to climb up over the threshold once it becomes clear that you are too low. If you always do a full glide approach and come in much steeper then as long as the glide speed is kept correct the sight view will quickly tell you if you are at the wrong height. Runway sliding up the runway = undershoot, runway sliding down the runway = overshoot. Glide speed good, threshold view at correct part of windscreen and throttle closed then you must be (correctly) above the threshold height. I haven't been to the place in the thread but it sounds a bit like Bembridge (coming in over the sea), where a high glide works for me.
I hope my explanation is clear.
Tin Hat ON.