speed, I discussed the full-scale Bücker because it had been mentioned before and I find interesting that its special snap-ability seems to come just not from a violent stall. Sorry for the digression. Your explanation of model stall maneuvers is very good, and I didn't mean the Bücker's behavior would translate to model size.
Of course you are right in that a biplane's decalage has to be chosen for a certain design point, a certain angle of attack that is. That is done to minimize drag and/or minimize stall speed, but for an aerobat there are different purposes. I just presume that your model has a good-natured stall because, if the lower wing stalls first, it produces much drag making for a pitching-down moment. With symmetric airfoils, that holds even upright and inverted. 1 degree decalage is not much, though, so it could be the airfoil as well that makes for a good stall.
Only in one point I disagree: Wing loading alone is not enough to compare models and full-size. You'd have to consider cubic (and for some movements even quad) wing loading because the airflow is the same if angles of attack are the same. Most models are rather heavy (seems to me) but 2-meter aerobats could be an exception since they are quite lightweight and are flown rather fast. That would indeed mean that biplane decalage has to be small compared to full-size. It's also true that models (at their low Re numbers) stall at lower angles aof attack and lift coefficients than full-size. But otherwise: same angle-of-attack, same airflow.
And yes, the original question has been not explicitely answered: Washout has nothing to do with biplane. It's just used to make a wing stall gentler (or reduce it's induced drag), independent of biplane or monoplane configuration. It could even complicate things on a biplane because it could make the lift coefficients vary over span. It may be even good for a non-tapered wing if it makes lift distribution elliptic and stall even more gentle. But that's not good for an aerobat since it works only upright and would be outright bad inverted.