Cement Board Underlayment Question

I hadn't thought of that, but I think I'm okay. The tub, by design, is supported by 4 4" squares evenly spaced. The floor itself is very solid. Either way it's too late now. I already have the BB installed. Thanks for the feedback just the same. Although I'd say my biggest aggrivation with projects is over thinking things, it's good to hear all the considerations.
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