I really don't think it is fair, is my point. See this 2-minute photoshop I did:
Light coloration is the actual header tank and aftercooler locations in the engine. If they were treated as if cooling components on a Dora, they should/would be modeled as it is in the dark highlights. I agree one-fifty is indeed enough in AH to damage it, but is it a guarenteed loss of coolant/radiator like it is on the Dora? If analisys was done on the AH P51 I don't think its close to acurate, but it would be inacurate in a way that would favor a pony driver in AH, not penalyse them like with the Dora.
My above image does not take into acount that the actual radiators are housed in the rather exposed belly scoop, nor the numerous lines that run to each independent system from the belly to the front and rear of the engine which would add a third rather large and damage-able area by a 50-cal area.
The lines if modeled IMHO alone would be the heel for the P51 in AH. Not only are they routed from one end to 2/3 the other, but (like how the Dora is modeled) easily damageable by a shot to the rear fueselage that doesn't penetrate forward the cockpit. IE: The bleeds for both coolant systems is located above the scoop in the L-fuselage. In the above image, roughly behind the wing on the left side in the region of the first black invasion stripe on the fuselage tail, behind the "3" in "C3".