Ariosto wrote:The position of the mics (close miked) means the room sound is reduced and therefore any bad standing waves are too.
This is an interesting point... close-miking will obviously reduce the overall audibility of general room tone. The reflected (reverberant) sound that makes up the room tone is chaotic and weak, so placing the mics closer to the wanted source will dramatically increase the level of the wanted piano sound and minimise the unwanted reflected sound.
However, close-miking is unlikely to reduce any problematical standing wave issues, and I've certainly had situations where simply close-miking a source didn't provide the solution! (Trying to record a double bass in a rehearsal room springs to mind...)
The issue here is the strength within the room of the low frequency reflections that create standing waves. To be aware of standing wave issues, there must be strong LF reflections -- most usually because the walls are brick or otherwise solid enough to reflect a great deal of LF energy.
So if that LF energy is being reflected within the room it will
interact with the direct sound and therefore create all those additive peaks and cancelling troughs we call standing waves throughout the room. That being the case, simply close-miking the source won't help.
What will help, though, is physically moving the mics around within the space to find positions away from the deep cancellation nulls or additive peaks.
So mic placement becomes a two-stage process: close enough to the source to minimise unwanted room tone, and then left-right /up-down /fore-aft to find positions that give the most uniform bass response.
Hope that helps.