That's a rather strict interpretation of some, unfortunately, loose language. We've always played it that if the stand can fit, it can go there. If there's room for a 20mm wide artillery unit there, there's room for a cav unit with 20mm of frontage.
At this point in the game, GW's not going to send out their rule police, so group consensus it.
Since Dave is right about it. lets get a group consensus about it.
Ole