I think it absolutely is important. Exactly how important, depends on the room.
If you're telling me the mic positioning is not affected by room geometry, then monitor positioning and the position of your head when you mix also would not be affected by studio acoustics. But nobody here believes that.
And before you talk about room reflections (i.e. reverb) having an affect on monitor positioning, but not a closely mic'd cabinet, (a) exactly how is the mic different from your ears; and (b) pressure buildup is what we perceive as modal problems in almost every room... and this pressure buildup doesn't go away just because the mic is close to its source. It all depends on where that mic is in relation to those nodal centers.
That said, it wouldn't affect the KPA as far as the core tone (e.g. distortion characteristics, transient response, etc.), largely just the overall EQ.
Just my opinion of course Change my mind.