Not every situation is the same but I found boosting a null created by a destructive interference from a reflection (like dash mids off a windshield or door midbass off a console) usually does not produce a favorable outcome. Though the RTA may show a slight improvement with lots of boost the sound will become strained - less effortless.

If there is anyway to at least tilt the driver under the grill or some other method so that it physically gets closer to the surface it's reflecting off - this will push the null up in the freq response and hopefully into another driver's passband (tweeter).

Here is the formula Patrick Bateman (John) posted that I mentioned earlier:

Start of Null Freq range = Speed of Sound (13500" per sec) / distance to reflective surface / 4

Here is the technical paper Souths1der mentioned above on dash speaker placement: