As I said in my previous post, the slide mods are changing how much air goes past the emulsion tube or bypass it.
Bernoulli's law says that the faster air moves, the lower pressure it has. The lower the pressure the more fuel gets pulled in from the emulsion tube. There are 3 small holes in the tube that give you idle, midrange and full throttle jetting.
If you want to make the carb suck up less fuel (leaner) figure out how to make the air going past the emulsion tube go slower. Adding bypass holes is one way, making the cutaway angle steeper is another way.
Since you're tuning everything with one jet, you also want to make sure that you are giving it as much advantage to be rich at full throttle, having a little air filter restriction means more pressure drop at higher rpm which means you can run a smaller main jet and be leaner at idle.
Eventually you get tuned to a point where the progression of the fuel delivery is too extreme for a Sha. Big porting and big pipe need a lot more fuel at wot and are much more load sensitive so you end up going to a multi circuit carb... Like the OEM one you removed, lol.