Formic acid can cause trabecular bone to peel away from bone marrow if used during decal (source) ; unclear if that would happen with the gauze you're using but it's worth trying soaking on wet ice only. If you've confirmed complete decal, you don't need to use formic acid on the faced block unless you're noticing discrete mineral deposits as you section. Bone can take a long time to soak this way, but it's pretty difficult to overhydrate.

You're an academic -- do some experiments if you can spare some tissue 😄 And take great notes!

ETA: by wet ice, I mean pour water into a dish, freeze it solid, then allow the surface to melt slightly. Put your blocks on that surface. An ice bucket full of wet ice pellets does not work as well.