One thing that might help is to look at the descriptions that people have used when they have also used the tag wheelchair=limited. This overpass query shows that in UK and Ireland (I’ve looked for wheelchair:description since it’s a bit more popular than wheelchair:description:en). Reducing that search to pubs gives this list. You can click on a sample of previously tagged things and see if the description matches your expectation.
Similarly, you can look for descriptions that contain “ramp” and do the same.
I’ve never been sure myself about portable ramps; I went with yes rather than limited for this one because it did look obvious and easily deployable, and the ramp was only needed for access to one part of the building.