osensei was fond of saying, 'even I don't know if I'm doing ikkyo correctly, or not'.
My idea is, thar almost no one does, The original idea was to stretch uke's loins, not just wrestle him downm then push him to the side, The original idea was to 'uplift' uke, in order to enter his attack.
Only Senudd, in sweden, seems to attempt to do it this way. Of everyone I've seen lately.
Of course, everyone still uses swordstrike for shomenuchi, which automatically negates any possibility of using ikkyo against a boxer, for example.