Common sense would tell you that averaging up into a trade that is a winner means that you will necessarily not make as much money on a trade because the full position was not on at the beginning. As for averaging down? Common sense dictates that this is not a good idea over the long haul. It's similar to just calling in poker and throwing good money after bad. In addition, if you average in, you'll likely average out which means that you"ll choke off profits.
When you average in, you create more decisions to make. This means there are more opportunities to be wrong. You don't want that.
I mean, the initial position is to my maximum acceptable capital risk. The second and subsequent trades are of the same size. Scaling in to most people means opening a small trade and then adding to it progressively until it reaches full size.