I think I'd go with style. It's a word that gets used in far too many different senses and contexts, but it seems to fit here.
Regarding system, I found these references:
Forms in Literary Systems:
If a literary system is the
environment in which a piece of text
comes into being, then literary forms
are the building blocks of that
environment. These forms are idiomatic
ways of writing, authorial tricks that
have built up over the years and
codified themselves into common
practice, tools with which to make
meaning. Taken in aggregate, they form
a system of rhetoric, a literary
and, from Poetics Today vol. 11 no.1, Spring 1990, the following sample of horrifying academese:
The "Literary System"
1. The Extension of the "Literary System"
Admittedly, the term "system" is tricky because of its so many uses. When we talk about "the system of literature" (or the "literary system"), one may easily be misled by the vernacular use of "system" in such expressions like "the political system," which vaguely denotes "the assumed complex of political activities." The use of this term in such current expressions is clearly a-theoretical: no commitment is made thereby to any specific theoretical approach towards investigating this "system." In polysystem theory, however, the term is already a commitment to the concept of "system" in (dynamic) functionalism, i.e., the network of relations that can be hypothesized for a certain set of assumed observables ("occurrences"/"phenomena").
I consider that passage a clear demonstration of the difference between "poetics" and "poetic". Also a crime against language.