using version v1.5.8 I have exactly the same issue with rockets falling short (ANF, Radar ranging on, I assume target motion disabled as its been noted that its off by default now).
Pre-release is at a 10-30 degree dive, 600-900kph.
Wait for the wings, fire rockets, and they always land about 80-100m short of the target.
(I note that the in-game tutorial says release when the range line flashes (below the target pipper). I tried that, rockets fell even shorter of the target.)
However,
I went and tested it in v2.2 and the miss was much smaller to the point I could put it down to an unsteady hand.
Based on the above testing, I believe there may be an error either in the hud symbology alignment or the rocket ranging calculations in v1.5.8. It would be good to get some Developer feedback on this though I note that 2.5 is around the corner and that may fix the problem.
In the meantime, I'm using Swordfish's method of offsetting the target 2 pipper heights below the pipper itself.