I think I'd be worrying less about cowl flap etiquette and more about flexible baffle condition, chafe strip condition and holes, gaps in the aluminium baffling to the engine.
Engine cooling depends on about a 4 psi differential between the top of the engine and below it. Cowl flaps serve to reduce the pressure below the engine by virtue of the venturi effect.
Job 1 is to make sure all the elements of the cooling system are in good condition and doing their job.
This goes for the oil cooler too. A significant proportion of the total cooling of the engine is done by engine oil. Make sure the oil coolers are clear with no bent fins and (one again) properly sealed.