It sounds as if the YHP might be jamming up somewhere. I can only speak from my experience on Footprints but when the YHP is released at the cleat on deck it goes completely slack and never jams up whether with full sail, or reefed. Mine is tied off at the halyard sling point on the yard, around the mast and back through a ball bearing block on the yard, down to the base of the mast, through a turning block and back to a cleat at the aft end of the cabin top. Whenever I lower the sail to reef, or drop it completely I first release the YHP because as the sail lowers past a certain point the yard begins to move aft on the mast. If I am reefed down by one to two panels the sling point still sits in against the mast, but anything beyond three panels down the sling point moves back a bit from the mast. Also worth noting is that with the sail fully up the sling point of the yard just naturally sits against the mast without any need for tension on the YHP.

Regarding fore and aft position of the sail on the mast, this can normally be adjusted by position of the sling point on the yard, and adjustment of the boom parrel, or line that forces the boom aft because without this line the whole sail will want to swing forward from the sling point. On Footprints I have a system which allows me to swing the whole sail across the mast when off the wind to reduce any weather helm.

Generally the swing point on the yard is at about 50 percent of the yard length. Moving the sling point further up the yard will allow the sail to move forward on the mast, but although moving the sling point down the yard will have the effect of moving the sail back on the mast, I don't know what this will do to the general balance of the sail in the way it hangs from the sling point. Maybe other members have experience of this. In the photo of your sail you seem to have quite a shallow yard angle with quite a long yard which might make it difficult to move the sail back on the mast.