The motor on the WS3000 is low power (Rutlands quote it as 1/5 HP - about 150W) - that's very much less than your typical sanding machine. I've occasionally tried applying small pieces of wood to the top of my WS3000 - the tool slows down dramatically, and juddered all over the place - I've long since stopped trying that experiment.
You might have better success using the under-port if you need to sand a narrow piece of wood to exactly one of the pre-set angles. That's not something I've needed to do, nor tried.
Good luck with the WS3000, though - IMHO it's a great piece of kit for most tool-sharpening tasks.