Well, at least starting with too much there is an upper limit.
There are all sorts of ways to alter the treatment even with only 2 variables.
I think I would try to establish as upper limit (probably already done- but lets see if the plants melt) and a lower limit (well, zero, but we know that will not kill the algae! Maybe start with the lowest dose suggested in this thread)
OK, here are some more numbers and algae treatment strategies. (all are using 3% H2O2 commonly available in USA)
1) Full tank of water with fish, plants and algae.
Turn off circulation, then squirt the max dose at the algae using a syringe or eyedropper. Turn on circulation after a few minutes.
Max dose that is safe for fish seems to be about 1 to 1.5ml H2O2 per gallon.
I have added that much H2O2, but not directed at any algae. I used it to boost the oxygen level when a pump had quit.
2) Drain the tank so the algae is exposed to the air.
Squirt H2O2 CAREFULLY on the algae, so as little as possible lands in the water. After most of the bubbling has stopped refill the tank.
Max dose that seems to be safe for fish is 2 ml per gallon.
3) Set up very good water circulation. Add power heads aimed directly at the worst algae. Remove nitrifying bacteria (filter media).
Dose with H2O2, and move the power head if needed to target other patches of algae.
Dose per actual volume of water, really make sure of it, not just assume.
Let it run for 15 minutes, then do 50% water change.
This method (high water circulation) seems that as much as 4 tablespoons per 10 gallons is safe. I have not done this, just read about it.
4) Here is something I tried: 1 pint H2O2 in a 5 gallon bucket with about 4 gallons of water. Dip durable plants (Java Fern, Anubias, and I do not remember what else. Probably Echinodorus) for about half an hour. Did not really stop the algae. I was hoping to slow the growth of some BBA while I was re-scaping the tank, so set up that bucket and soaked the plants while I moved some rocks and driftwood around. Did not seem to work. A little bit (maybe 10%) of the algae turned pink a day or so later. Plants were fine.