When running 2.2 wheels, I only use the lower holes. When running older 2" wheels, I used the upper holes. The camber link also moves on the inside to keep the equivalent location. By doing this I can keep the chassis the same height from the ground at the same arm angle orientation. Basically, the roll center and ride heights can be made the same with different size wheels.
What I like about the rear end geometry of that car is that when using the lower holes, at arms level (they are straight arms, which helps), I am also at driveshafts level and I set camber links level at this point as well. The links will just be shorter than the arm length pin to pin distance.

Team Associated's suspension geometry goes back to the B3 for production but to the 89 and 91 IFMAR cars for concept. Those concept cars used RC10 rear hubs which placed the driveshaft low towards the hinge pins, much like the upper hole on the JRX hubs. Why were they so low? The simple answer is that they had to be back then. The car originally came with 1.6" rear wheels. The diff gear is going to be a certain size and will need a certain amount of room which will dictate where the driveshaft height is. Put those together and you've got the driveshaft angle. Incidentally, the original 6 gear box had a lower driveshaft height than the stealth did. As they evolved the gearbox design to use a slightly larger diff gear, they lowered the bottom of the gearbox into a hole in the chassis to give clearance while maintaining that driveshaft height.

As wheel sized increased, the rest of the geometry was never really dealt with and their modern cars are descendants of that old geometry. Our Raborn rear arms for the RC10 were typically also used with our rear hubs which were essentially Losi copies and they worked far better. That's why I have a bin full of them. You run the lower hole with the 2.2 wheels, putting the axle closer to parallel with the arms and fixing the roll center location. This is especially important when running lower ride heights.

What I'd really like to do on my B44 is to make a new rear arm that is totally straight without the upward bend at the hub. Then make a new hub that extends down to it, lowering the outer hinge pin location. This would fix the roll center for high grip tracks where low ride heights are used. I doubt I'll ever do it but I truly hate the back of that car.