Happy is the main lexical predicate here. It takes one argument: an experiencer--John. Tall takes one argument: a theme: Mary. (12) *John is being tall. (13) *Mary is being fond of red roses. (14) ...
Prenominal adjectives precede the noun its modifies and it must occur in the same NP (see L222). Consider the italicized parts of the following two sentences: (1) The student is eager. (2) The eager ...