Aidanf, fascinating post. I too had simillar problems prior to my solo, and PPRuNe replies were most helpful.
I'm still not quite sure about the exact science involved in making an accurate safe landing, but here are a few of my observations:
1) Well trimmed accurate approach certainly lightens the workload prior to landing.
2) The more circuits I completed, the worse my performance. With hindsight, I guess the release of "fight or flight" hormones after just turning onto finals wasn't helping. T think this may have been cocking up my peripheral vision, (and hence cocking up my height judgement), when it was needed most. (Over the numbers). In this respect, "looking at the far boundary" certainly helped me, although I find I rely on this less and less now.
Interestingly, I find my performance improves when I am not accompanied by instructor or examiner. (Or is this my perception?).
Anyway keep at it. Remember those hill starts/three point turns/emergency stops when learning to drive ? Second nature now.
I think my posting on the subject was around Feb 2002.