The science of Split Shot----->More is better!
When the water is deep and the fish are deep, more is better. When the water is fast, more is better. You do have to get the fly down to the level of the fish.
For midge fishing in slow water, depth will likely be no more than 3 or 4 feet. If you look at the popular spring creeks, the tail waters like the San Juan and Big Horn Rivers, it will likely be in the 1 to 2 feet area.
For micro midge fishing, the split shot should be no larger than #6.
When more weight is needed, install 1 or 2 of equal size about 1 inch apart.
Distribute the weight on the tippet so it makes a minimum of splash.
Split shot sizes: These do get small and are available down to size 9. It takes practice to install number 7, 8 or 9 shot. You are going to drop them in the water. But, you do get a few hundred of these in that package of small ones.
Practice attaching these to a tippet so you don't waste time on the river trying to get it to stay put.