I think every vital poetic movement has a very specific dialectic which drives it to expand and develop. For example, Imagism comprised terseness plus concrete, usually visual, detail; Langpo, social contextualism (often Marxist or post-Marxist), plus vernacular contrarianism ("I hate speech").

Umbrism's sharpness and engorgement could be such a dialectic. I'm thinking that sharpness could mean something like "One word ends then another begins"; and engorgement: "Every phrase shall be pregnant with meaning".

K. S.