I used the scoring knife and the Hardiebacker screws
I do have a separate question on how much compression there should be between the hardie board and the subfloor? Using the 1/4" trowel would leave a 1/4" of space but using the screws it pulled it tight when the heads went flush with the board.
What is the proper way or better, how should I properly set the hardie to the subfloor using modified thinset and screws? I'm securing the 1/4" in a few days, i am going to try to use the roofing nails again as my thoughts are that since it is thinner the nails wont bend, they might actually go through the board.