Good questions guys.
Ever since I discovered that the TC-1630 pattern came up a bit short compared to Frank's solid fuselage casting I've talked to several guys who cast a lot of stuff and the consensus is that the TC-1630 is actually intended for thinner stage pouring and layups, and while it has low shrinkage in thin cross-sections it actually gets quite "hot" when it's used for very thick parts. The hotter the resin gets as it gels, the more shrinkage you get in the casting, generally.
This is why the wing patterns I have, which are also cast in TC-1630, are the exact same size as the wings Frank started with. They have a much thinner cross-section, and so the resin shrank very little.
What I think happened is that because the solid fuselage requires such a large amount of resin that ends up being very dense, the TC-1630 actually shrank a little bit more than the resin Frank used to cast his solid fuselages. The data sheet for TC-1630 does say that it can shrink more in thick sections.
It's the same reason why Frank's hollow fuselages are larger than the solid ones even though they came out of the exact same mold. More resin, hotter cure, more shrinkage.