I will try to avoid controversy here. Not easy sometimes. I do not believe your idea will work to raise coolant level a little at a time.
I believe you are doomed and have to pull head again. You have two potential problems. Cracked eroded head or (very likely) head gasket not sealing on sleeve flange. Flange too low or too high or wrong gasket. Like I indicated before, mix ups on those gaskets has been a problem .
Maybe Slater will chime in. Very knowlegable.