  We give a non-FPT lower bound on the size of structured decision DNNF and
OBDD with decomposable AND-nodes representing CNF-formulas of bounded incidence
treewidth. Both models are known to be of FPT size for CNFs of bounded primal
treewidth. To the best of our knowledge this is the first parameterized
separation of primal treewidth and incidence treewidth for knowledge
compilation models.
