in my roder's 'a history of the concerto' it says 'the adagio sostenuto in E major opens in a manner reminiscent of the slow movements of rach's first concerto and tchaikovsky's B-flat minor piano concerto; that is, with a short orchestral transition from the key of the first movement to that of the second. the flute and the clarinet are given important thematic material. the more animated middle section of the ternary form centers in A major.'
from all this i gather that he's still working with fifths (albeit V/V) or subdominant V) from E to a minor (E being the V of a). but, the minor thirds are important, too (f#minor to a minor). at least now, u can compare different analysis not only of the rach 2nd, but also the rach 1st, and tchaikovsky to get some idea of what kind of patterns are used. there is obviously some key connection - but then there is a sort of step by step connection in places where it moves up a major second. sometimes, don't u think it is like those pattern problems in mathematics where they ask 'what comes next.' u see a pattern and u have to figure out it's chain. transitions are easier.
about the first rach pc - 'the short slow movement, prefaced by an orchestral transition to D major, recalls a chopin nocturne with russian overtones. it becomes increasingly decorated as it progresses (so if u are analyzing - u start eliminating decoration and calling it that?)