You should add another upgrade similar the camoflauge upgrade in that with this upgrade, everything inside a force field does not get rendered from outside it (obviously only an upgrade only for the area projector, be cool if it would work with the dome upgrade and only hide blocks in the dome... and maybe render water when combined with the underwater upgrade). Also as an added visual effect, blocks inside the field could be made slightly transparent (that's just my opinion), and preferably having blocks in other (cloaked) fields belonging to the same core visible from inside a field.
I have no idea how difficult it would be to implement this, although you could use the way the sides of glass blocks are not rendered if that side is touching another glss block.
This is just a somewhat complicated method of suggesting force fields should be able to act as cloaking devices.