Another thought is the supply side of the VE... . if the guide pin is protruding too far and/or it actually extends deep into the AFC housing the fuel leak will result in a drop (small as it may be) on the supply pump side.
This supply side pressure has a direct effect on the pressure variation(s) within the high pressure head.
just a thought... .
pb... .
edit: if you really want to try something along this line, then have a modified pin installed, crank the smoke screw all the way down until you can assure the guide pin will shoot out and immediately onto/into the deepest part of the cone... this will give you the same results, more or less, but will prevent the guide pin from actually 'bailing' on you... you may even need to use a longer screw if the smoke screw is too short... I've never checked that myself.