I’m not sure I understand how you’re ending up with this 20% statistic. A bare build platform will not retain a significant amount of resin. If you’re talking about the platform before the print is removed, I could imagine there’s a little resin to be saved if you let the print sit over the resin tank for a while before you try and pry it off (which I do sometimes. But I just leave the print on the platform in the printer for a few hours. given the viscosity of the resin, angling the platform shouldn’t make much difference).
20%? That’s a lot. Doesn’t feel like a “real” number. Do you have some data you can share?