what are your temperatures specifically? I know you said your temperature is controlled, but is it controlled by a thermostat? Also, I think 2/3 covered by the heat pad might be a little bit too much. I was always told 1/3-1/2 at most to create a good temp gradient. Your BP is probably either too warm or just wants to hang out in it's cool hide. I have a one who likes her cool side too. She'll move to the warm when she needs to, but lately has been quite fond of her cool hide.