I found that by closing the "kool dump" in the bedroom and also all the ducted vents in the rear of the coach, that most (all) of the cooling capacity of the rear AC is channeled to the front part of the coach.
Sort of a "helper" for the front AC on super hot days. Like 111 in Pahrump, NV last month!!
And since I'm rarely in the rear if the MH during the day I don't need the BR AC until bedtime.
Even so, the "kool dump" setting seems to be the most efficient, except for the additional noise.