I've found the instruction book, which says that the regulators are nothing to do with the drones, they are 3 chanters, which do lie across the piper's knee in the way I described, and have keys attached. In a concert set of pipes, which means they're pitched in D, the bass regulator has the notes g, a, b, c, an octave below the chanter. the tenor regulator has the notes d, f sharp, g, a, in the same octave as the chanter, and the treble regulator, the smallest, has f sharp, g, a b,c, also in the same octave as the chanter. The piper makes up a chord by playing a note from two or three of these regulators simultaneously. So the piper's chords are going to be made up of combinations of one note from each of the above groups.

They are designed to play in the keys of d, g, and e minor, but they are not tuned in the modern 'well tempered' way which electronic tuners show, or by which the frets on stringed instruments are placed. This is because if some of the notes were played to the modern pitch at the same as the drones are playing, (they play the note of d on d pipes) there would be a clash of notes, for instance if you played as d drone at the same time as a modern c note in the tune, it would sound awful. So the c on the pipes is flattened (I think) to make it sound better. Apparently b is changed as well, and maybe a few other notes, to make it possible to play all the notes on the instrument without jarring clashes.I am told by a piper that minor chords have a tendency to fit alongside pipe tunes more easily than major, don't know how true that is. You will come across flat pipes which are those tuned lower than d, this wasn't done so much out of badness but these are the original pitches of pipes, it was only later that somebody decided to make them in d so that it was easier for other instruments to play with them, as far as I know. The lower pitched pipes are easier to maintain, as Cliff says D pipes are a constant battle to keep in tune with continuous reed adjustments and changes in pitch, frustration and bad temper.

I'm glad you care enough to listen and try to get an accompaniment that complements the tune, there are plenty who don't bother to try.

All the best, Liz