Closet flange hub threads onto 3" drain pipe, and is screwed down onto previously linoleumed subfloor (I replaced bad area about 2x3" area surrounding the toilet so it is bare plywood). There is NO play in the pipe to allow it to move upwards. I will be installing hardibacker and standard 6 or 12" ceramic tile, which will raise the finished floor 1/2 to 3/4" above the flange.
Googling reveals two possible solutions: get a flange extender kit to raise the flange, or just use an extra plain wax ring over the one with the horn.
Some say that extra wax is sufficient; some say that it is a band-aid that will eventually allow leakage.
Any experience or preferences - what say you?