  We establish a macroscopic description of the splay--density coupling in
semiflexible main-chain nematic polymers with hairpins, using a vectorial
continuity constraint for the "recovered" polar order of the chain tangents and
introducing chain backfolds (hairpins) as its new type of sources besides chain
ends. We treat both types of sources on a unified basis as a mixture of two
ideal gases with fixed composition. Performing detailed Monte Carlo simulations
of nematic monodomain melts of "soft" worm-like chains with variable length and
flexibility, we show via their structure factors that the chain backfolding
weakens the splay--density coupling, and demonstrate how this weakening can be
consistently quantified on the macroscopic level. We also probe and discuss the
deviations from the noninteracting gas idealization of the chain ends and
backfolds.
