2 cents, YMMV, etc, but FWIW, for buccal mucosa/RMT, in the absence of floor of mouth, soft-palate or tonsil involvement, we almost always treat post-op unilaterally, even for pts w T3-4 disease, as long as no evidence of contra-nodes pre-op.
Ipsi RP nodes get covered incidentally as part of your masticator space coverage, but we don't really push high RP coverage anymore (we did until about 5 years ago). If nodes were big in level 2, that can drive RP coverage as a function of parapharyngeal space, but broadly would cover lower ispi RPs, ispi 1B-4, with level 5 almost always incidentally as function of the dissected neck low-intermediate dose. IA coverage depends how close to the lateral commissure primary was; if it was > 2cm, we often omit or cover w elective if undirected. If dissected it gets intermediate/elective dose.
Attached are indicative anonymous screen caps from a pT2N1M0 buccal mucosa case w a single node+ in level 1b...hopefully useful.