> Is this about where along the string the hammers are hitting?
I suspect you are right, I studied a bit of classical guitar and I know for a fact that plucking the strings near the bridge or near the fretboard creates very different sounds. It is probably a similar problem with pianos.
If I understand correctly, I think the usual strategy is for the hammer to strike at the spot along the strings that's the nearest 7th harmonic node from the end. The reason being that by striking there you don't set up as much 7th harmonic vibrations, which don't mesh well with 12-tone equal tempered music.
I suspect you are right, I studied a bit of classical guitar and I know for a fact that plucking the strings near the bridge or near the fretboard creates very different sounds. It is probably a similar problem with pianos.