The sweet spot is a body temp between 84 and 88 degrees. It has nothing to do with movement between hides. Frequent movement between hides indicates the animal was not comfortable in the hide for some reason one of which may be temperature. Staying in one hide or the other for long periods is also problematic in that it may indicate the the other hide is too hot or too cold. When we supply a gradient we allow the animal to heat and cool itself. Most people end up having to do this because controlling the ambient is not practical.
Well my ball tends to always be in the cool side. Temps are 80-81 on cool and 89-90 on hot.