Ask those with experience in placing microphones for piano recording and the chances are you will hear of it being an art form rather than a reproducible technique. There is truth in that – as the variables are enormous. On the other hand there are some tried and tested methods, or rather some useful guidelines.
Our experience with an upright piano is demonstrated in this Chopin and Bach link. We used three microphone pairs and selected a mix of each in the final editing. The open lid in an empty church was a bit heavy on the echo though.
For jazz groups and for gigs where instrument sound separation is required for later mastering, close ‘miking’ is essential – but might not be best for smoothness and ambience suited to quieter or classical music situations. Under those conditions, a pair of mics at a half to one meter distance (fully open lid) will give very decent results. However, if there risks to be people noise, then closer placement might still be necessary.
Here is a set-up which we used for a 2017 jazz group recording – a single pair of Neumann condenser microphones. Actually the sound was excellent; results here. Rules of thumb: place microphone pair above where the high and low strings cross – spread apart for better width pick-up – raise for more body.
A Swiss Radio (RTS/Espace 2) recording we attended at studio 15 in Lausanne – Enrico Pieranunzi trio – piano with 8 mics. (this blog update, 24Oct2017) :-
DPA’s “d:vote” microphone stereo kit for piano — Esteban Castro at Montreux and manufacturer’s image :-
At the AMR/Sud des Alpes concert room with the Grupetto :-