Good point in the issues related to the taper of the wing.

Given that we know the lift coefficient for the root area will be up around .7 to .8 you may want to look at what angle of attack it takes to achieve that. Then lower the angle at the tip via washout to get the Cl down to around .2 or .3. And THEN use some fairly extreme differential on the controls as well as plan on using some rudder along with aileron at lower speeds.

A buddy of mine built a super light 36'ish inch span SPAD 13 for electric. In his quest to fly it at a scale speed he spends all his time about one notch away from a stall. Then he wonders why it produces a lot of adverse yaw even when he used extreme differential. I kept telling him he needed to use a little rudder with the aileron but he tried to avoid it. Finally he set up a mix and found that it worked much better.

This issue with the ailerons is a biggie with sailplanes as well. I've seen some nasty tip stall and snaps because someone got greedy with the aileron at low altitude and while trying to "stretch" for home. Low and slow calls for miniscule control inputs on the ailerons in any design and far more so with sailplanes or extreme tapered wings.