avoiding hot end

[Preston]

hi i have 2 afb's currently and they are avoiding the hot end (85f) of the enclosure and like to hang out in the coolest area which is 72-74f. the water source is in the middle which sits at roughly 80f. the enclosure is 100cm long so they have moved a fair distance from the heat source.
i thought these guys would be basking under the hottest temps? a lot of people recommended 85 or even 90f. i guess they appreciate more milder temps? the humidity is the same on both ends by the way.
cheers.