That's an interesting observation. I use %PC for buy dollar amounts but use %shares for share count in selling. I guess this makes me AC/DC!!!
I'd have to think about why it is that I've been doing things this way, but that would require some asprin!!!
I seem to recall one being more aggressive than the other on the buy side and visa versa on the sell side. AC/DC seems a good idea to better keep both sides somewhat more evenly balanced.