Chris,

Ross Seyfried had a similar problem of his double rifle regulating but 5" above the aiming point. He wrote about it and his loading solution in DGJ Vol 7, Issue 3 (Autumn 1996), page 53.

If using a different load didn't work, I would be inclined to replace the front sight with a higher sight as the regulation is great. Of course, I would keep the original front sight to pass on to the next custodian.