I agree that everything I've read here sounds nose heavy. You're toward the front of the CG range, so move it back a 1/4 inch and see what that gets you.

On the thrust line, the relation to the cowl isn't important aside from looks. Put a level (incidence meter is more accurate and easier to use) on the horizontal stabilizer and shim it on your workbench to get it level. Then use your level to see how far off of 90 degrees your prop is compared to the stab. I would expect 2-3 degrees of down thrust and maybe 1degree of right on a model like that. If you have up thrust that would explain your diving glides (or at least contribute to them) as your tail trim would be compensating for the thrust pulling the plane up. Measure it (and keep good notes in case you need to go back) and only fix it if you truly have up thrust. Then do a thrust line test as described in the trim manual.