FWIW I don't think a little block at the masthead is really necessary. You could just as easily use a polished SS ring suspended from a small strap sewn into the head of the sail with a wear patch on the sail under it to protect the fabric
from chafe. The diameter of the leach line is so small and it would have so little contact with the ring, the friction would be negligable.
With the idea I described earlier, you could add a 3rd reef line just as easily. They could all pass through a single
ring together as the 1st, 2nd, and 3rd reef leach lines would be slack when the sail is not reefed and each subsequent line would slacken as the next in order is taken up (i.e. the standard leach line would go slack as the 1st Reef is taken; the 1st Reef as the second reef is taken, etc. etc.). If necessary, you could also have four over lapping rings at the masthead with the lines led through them starting with the full sail leach line on the bottom then 1st reef, 2nd etc.
The one benefit to the foregoing arrangement is that one would be less inclined to forget to release each leach line in turn as the reefs
are shaken out as they would be right in front of one's eyes. I could see one overlooking a tightened leach line secured above each leach reef cringle, however.
Forgetting the foregoing, after pondering the matter somewhat more, it seems to me that you may just not have taken up enough of the single
leech line while reefed. I can see the sail gathering up somewhat but eventually, the cloth cannot be further compressed at which point the line has to start tightening the leech above the cringle. The only thing is that you might end up with rather a lot of spaghetti at the mast
by the time you get to the 3rd reef.