I have not loaded 700x for years, but I don't recall having issues with it. 800x is known for metering issues. One thing that MAY help is a powder baffle, the red PC (pattern control) baffle seems to get the best reviews. YMMV.
Another 'trick' to loading on the single stage is to size, deprime and prime all the hulls, then go back and drop powder and crimp them. Supposedly it speeds up the overall process and helps with getting a little more uniform drops. Also, the more consistent your cycling the machine, the more consistent the drops will be. I load on a progressive press which is bolted to a stout top, which is bolted to the wall, I don't get much variation in my drops.
If your drops don't match the charts I wouldn't worry about it, use the bushing that works. If your drops just have to much variation - maybe more than +/- 0.2 then I'd worry about it and try to sort out what the problem is.