There's no formula that I know of. It comes down to a case of "the last model was OK but it was a little slow to respond to rudder so let's put in a little more dihedral". And to some extent the amount used is linked to how heavy the model is and how fast it flies. A light but fast flyer will respond to yaw angles with a faster roll rate than a slower and heavy model.
And there's no doubt that putting the greater angle at the tips results in a stronger roll rate than using simple V or gull wing dihedral. In fact gull wings typically roll very poorly in response to yawing with rudder. So while a poly, simple V and gull wing may all have the same total value of root to tip dihedral the nod certainly and enthusiastically goes to the polyhedral option for getting the most rolling couple from a given yaw angle.
This would suggest that going to a multi break 5 or 7 panel wing would be even better. But I'd suggest that once you are at a basic 4 panel "Gentle Lady" wing layout that adding more dihedral breaks is only going to give you a very little extra for yaw to roll effectiveness. The 5 panel wings are popular for a lot of RES models. I'd suggest that the main gain over a 4 panel wing is the use of a flat center for an uninterrupted center panel wing spar and a natural place to mount a single spoiler surface and control linkage for simplicity.
So why would we bother with more than 4 or 5 panel arrangements? Dave Thornberg suggested that perhaps the elephant ear Wolf wingtips are somehow more efficient at contraining and using the flow of air around the dihedral break. Do they? We'd need to do some serious wind tunnel or thread tuft experiments to find out if his claim is true or not. But given that we know there's a significant amount of span wise flow on any real wing I'd say that using more dihedral breaks of smaller angles between panels SHOULD result in less drag. Ideally an RES model should likely use a smooth elliptical curved wing like that found on the old Hobie Hawk. And is it better to break up the tripped air that flows over these joints over more joints of smaller angle or is it better to "just get it over with" and have one mid span dihedral break? Not having access to a wind tunnel I'll have to invoke the Heisenburg Uncertainty Principle on this topic and say "I just don't know.... "
Getting back to the BoT.... For some years I flew a somewhat heavy BoT and a T tailed RO-8 2 meter. Both shared the use of rather short tail moment lengths and both have the tendency to "level and leave" a thermal if I slow down a little too much. When I got into electric flying I built a new fuselage for the RO-8 wings and stabilators. I made the new fuselage about 2.5 inches longer and reduced the size of the fin and rudder by about 15 to 20% to make up for the added length. The longer fuselage even with the smaller fin and rudder totally changed for the better how the model flew. Granted some of this was the slightly higher flying speed needed by the weight. But on two occasions I had ballasted the old original glider for windy days and the new electric fuselage let the wings fly SOOOO much better. The model was more responsive to the rudder inputs. Some of the wing wobbles where the tips wobble around for a moment or so that occured on both the BoT and short glider RO-8 when flying with lots of rudder in turbulent conditions was gone. The "level and leave" if the model was slowed down in lift was gone. All in all the model was far more delightful to fly in all conditions.
Based on all this if I were to build another BoT the one mod I would do is to stretch the fuselage in a similar way as what I did with the RO-8. My thinking is to make the tail about 2.5 to 3 inches longer and slightly reduce the size of the fin and rudder by maybe 10% in compensation.
As for the dihedral adding another 1/2 to 3/4 inch to the tips would likely not be a bad thing either. While I suspect that much of the improvement in the yaw-roll response would likely come from the tail length increase a small amount of added dihedral would be like adding suspenders to a better fitting belt. And a paltry 1/2 or 3/4 inch of added dihedral would not have any significant bad effects in either appearance or added air drag around the dihedral joint.
The BoT is known for needing a fairly sizable lump of lead in the nose. So along with the tail length increase adding an inch or little more to the nose would not be a bad thing. That and working hard to keep the weight of the tail under control by building light and then "carbon it up" with a layer of carbon cloth and resin over the whole fuselage and especially over the tail. And building up the rudder and fin instead of the solid sheet versions in the plan and kit should further work to reduce the need for lead in the nose. And for contest work with the typical landing "arrivals" it would not even be a bad thing to include stiffener stringers of carbon flat rectangular rod inset into grooves in the fuselage wood before the cloth and resin is applied. The fuselage wood could be nicely carved and sanded and then the stringers inlaid in grooves cut into the surface. A slick little grooving tool can be easily made by cutting and glueing pieces of coarse tooth hacksaw blades together to make a short "wood rasp" for a job of this sort. Then the carbon cloth can be pulled to produce a long axis diagonal weave pattern wich both lends some added longitudinal strength but also gives a lot of torsional stiffness by acting like diagonals joining the main load carrying stringers together.