i have only used rockwool to dirt once, they were the one inchers like what you have, i started them in an ebb and flow but changed my mind.
it was lr2.
when i took them from the ebb and flow they were one week old and only a little bit of the roots were coming out the bottom, i took the plastic off and burried em to about 1/8 inch below the surface, at week three i pulled out some males that had shown sex and roots had come out the sides and the bottom of the rockwool about 6-8 inches (besides the finer roots that broke off).
i think it would be best to take the plastic off just so they can grow where they want.