I think pyramiding in, i.e. successively smaller sizes works best when you have some arbitrary position-adding point - like if you decide to add to your trade every 50 pips - so that the arbitrary add-on doesn't wipe out all the gains from the intial position if it goes against you. However if you treat each entry as a single trade, only adding to your position at a point when you would have made that trade anyway if you weren't in the market, then size shouldn't matter - you just do whatever size you would normally risk for that trade.