I would have to disagree with that. If the tire is NOT fully seated one is wasting their time trying to balance it. But, full disclosure: I have worked with balancing things more than I care to remember. I was a NVH specialist (noise-vibration-harshness) who trained professionals on how to cure vibration problems. I got spoiled having a lot of high dollar specialized computer driven machines to solve these problems. A motorcycle wheel seems pretty tame compared to some of the issue we had to deal with.One small suggestion: Don't seat the tire bead until AFTER you get it balanced. That way, it's easier to rotate the tire in relation to the wheel if you need to adjust for a very out-of-balance tire.
Moment arms: You can read the complex physics of these but in simple layman terms the further a weight is from the center of rotation the more it affects the balance.
Weight on on spot, both sides of the rim or on the spoke? Some bikes will have one weight attached to a spoke next to the rim. Most of these I have seen were chrome plated and on Harley type bikes. Some will split the weight and put half on either side of the rim. (not a bad idea...usually). On automotive applications we might put weight on the inside, outside or center of the rim. A high end balancer will let you program how you want to place the weight and then do its best to figure out what to use for your choice. On the wider tire of a car or truck you can have a problem with one side being heavier than the other and the weight needs to be put on the rim on one side only to counter that.
One big truck tires, due to that moment arm thing, we actually have glue on weights where we run the wheel assembly, mark every thing and then break the tire down and stick the lead weight on the INSIDE of the tire against the tread. This allows the weight to have more influence due to it being further away from the center of rotation. You need some "professional grade" machinery to do that sort of stuff.
How do you know your rim is in balance? Did you check it? I spent a lot of time diagnosing, and teaching classes to professionals how to diagnose, the odd ball vibration problems. I had the best gear available and all the resources to hand these problems. We were always able to resolve the issues but sometimes the problems were much bigger than just a tire or a rim.
My point is simply this....motorcycle tires are not very wide nor heavy. Don't over analyze balancing them. Also remember doing static balancing on a stand is more hope and prayer than science. There are a lot of dynamic forces that don't show up until the wheel is spinning and even more so when its spinning while being loaded. As I use to tell my students, "We can perfectly balance a square wheel, but will it ride smoothly?". And then there is "RFV", Radial Force Variation, where a wheel is round and in dynamic balance but vibrates under a load. Look it up....again, something that requires high end equipment to find and correct.
My approach is simple: But a high quality name brand tire. Mount it and seat it completely. Put it on a stand and spin it to insure the rim is straight and the tire runs true. Do a dynamic balance on it and go ride on it. You will most likely be fine. If you do have any bad vibration problems you likely have a tire issue. Break down the tire, move it 180 degrees on the rim and repeat the balancing. If there is still an issue, try another tire.