Yes absolutely.

UTHs are radiant heat it is line of sight. This means in effect the floor of the tub is the heater for the tub especially when you account radient heat travels though air without heating it. The more substrate on the floor (the heat source) the more heat is held at the floor. As you know organic chips (aspen coco coir cyprus ect...) are good insulators even newspaper will make a difference. This is why it is difficult in holding ambient temps the UTH has little effect on them. All your planning has bought you 5ºF of ambient temps. It is not that much, in the end, it is enough but your room is not that cool (I call 68ºF normal above warm below cool )

I personally would like to see ambients a touch higher myself. 78 is fine but will your room hold 72 or higher and not dip below for long? This is my issue during the winter I have average of 68ºF with cool snaps dropping to 64-5ºF for a week or two. I plan for the cold snaps rather than the average.