I prefer to call it "trade stacking"....When I start a progression, I place my "anchor trade(s)" near the beginning of the trade cycle. These will have a very tight stop...mostly mental, so as not to show my hand. The anchor trades are usually larger in size than the later added trades. Once the trade initiates and price moves in my direction, I do not scale in, I add additional trades. I have used a scale in script with pending orders when action is fast and trading multiple pairs, like news events, but in this case, each trade was a manually entered market order.
I will take profits at the sign of a retrace, bank the pips and wait for a new progression to begin the cycle over, as I have done with this pair.
What you are doing is similar to what I do, yet quite different. I believe you look to spread 1-2% of total risk across a spread trade pattern. What I do is to add individual trades, each with their own risk factors. There is a big difference there. While it may look like high risk to many, the risk of each added trade is already mitigated by the positive equity in the preceding trades. At times, with a large progression, I will close the older trades that are well in the money, while rolling into a new, replacement trade should the cycle look to continue. The progression depicted in the chart returned 500 pips, give or take 20, when it was closed. With a scale in, those would be fractional pips. With stacking, they are a true pip count as each stacked order is almost as large as the initial anchor trades and would be the equivalent of placing those individual trades on other pairs. I prefer to have a bunch or winners on one chart as opposed to having a bunch of winners, spread across many pair.
I've posted many examples of this in my threads, but each person needs to work with what is comfortable to them and their accounts.
Don't ask for numbers, ratios, %'s or any other formulas as to how I compute the trades as I don't use any, I just trade. When laying on additional trades, they come from S/R levels and the like...places where price pauses or retraces a bit before continuing on its way.
I've discussed several ways to protect the trades, like setting a hard stop above a retrace and locking in profit should you wish to hold the trades or just close them out and reload as I am doing here.
Since I don't auto-trade, I have no need to figure out the math to have an EA do this and I don't need to have money exposed 24hr a day to be profitable. Trade the London-NY sessions and look for 25-50 pip moves.... it really is all you need. BTW, I've got 2 trades started in the new progression as I type this and will build this position into the London session, looking to reverse it in the NY...
CJ