Well good to know you're still working on this. I have no idea how well the "only two forcefield problem" is in singleplayer. My concern is in multiplayer. However I think it's maybe a Minecraft issue itself? Since MFFS is also giving me (my server) the same problem. Could it maybe be a conflict between the two mods (not block or item-wise)?
This makes things tricky since then there's no real way to restrict areas and protect buildings without-fail without using bedrock and other indestructible blocks. And bedrock and the like just isn't fair.