Well, 'awen' is probably a modal (M) rather than just a verb (V) but that doesn't change anything significant. Most tp words can (and many do) occur in several roles. The trick is to find a typology that allows us to predict with some precision what will happen when a word from one class is used in the native role of another class. Some general rules are clear, other phenomena don't yet seem to fit any roles. 'awen', as a vt, means "to keep, preserve", possibly also to "to guard, keep safe" and so on. So, as a noun, one expects it to mean, inter alia, "canned goods, preservation, waiting, ward, constancy, inertia, ..." As a modifier, one would expect "constant, steady, persistent, safe, enduring, ..." "sitting" doesn't seem to come in and that is because tp doesn't do collapsed relative clauses well (at all, probably). But there are a number of other possibilities, I'm sure, both for 'awen' and for "person at the head of the table" (itself a problematic expression). I would just use 'lon' since it is a very temporary job.
To be sure, several tp phrases have canned meanings that are hard to get around. But the official line is still that these are nonce forms pressed into service for immediate needs and not fixed. And we can tear them apart, in most cases, with a bit of context (as always). I think they should all be listed (have you done a run to find such critters? My list is hopelessly dated.), but officially as exemplars of how to do it, not as rules about what is to be done.