One of the things I have noticed is how Prevost delivers a coach and its mud flaps. I have no specific information to verify my theories, but just a sense mud flaps play a role in maintaining engine temps.
My first two coach had none or very little air flow openings through the engine rear doors and my guess is the air drawn through the radiator by the fan was forced down and out or across the engine to the RH door where some went down and the rest went out the door. That suggested to me that I did not want anything to block the flow of the exiting air towards the rear and anything that could contribute to a low pressure area such as wide tag axle mud flaps would encourage the needed air flow.
My current coach is an entirely different animal in that air passing through the radiator cannot escape downward because a Prevost installed baffle is in place and air has to make a turn towards the rear doors or cross the engine where it can pass out the side door or through the rear door. In that case a full width flap contributes to the creation of the low pressure area immediately behind the engine rear door slots drawing hot oir out.
My reason for babbling is because heat rejection is a critical need and if mud flaps are originally installed I would not modify their location or size because I am convinced they contribut to engine cooling.