No, in fact, all my positions are identical in size, which is the maximum % of account capital that I am prepared to risk. A lot of people use the 2% rule so if I was using 2% as the max risk, the first with-trend trade is 2% and I immediately set an identical entry order of another 2%: if that is triggered I set an identical 2% entry order and so on.
The only trades I initiate are trend-following and every one of these is a potential major winner (I recently increased a Dow long to 7 parallel positions, each of identical size). On the other hand, no trade or series of trades, whether its 2, 5 or 7 or whatever, can ever lose more than the initial £ risk from account capital.
I am sure long-term I will not get into many trades that can be added to another 6 times, but the small fraction that do will do great things for my profit levels.