Usual practice has been to describe the post-sunset rise (PSSR) of the equatorial F layer with the vertical drift velocity measured overhead, as a function of local time, by a ground-based sensor. However, with the finding that large-scale wave structure (LSWS) develops with its own eastward polarization electric field, during a PSSR, the measured upward velocity must now be thought of as containing two components, one associated with PSSR, and the other with LSWS. This distinction may hold the key to understanding the lack of correlation, on a day-to-day basis, between measured vertical drift and ensuing plasma structure in the form of plasma bubbles. Measurements of backscatter from the bottomside of the F layer, using a three-beam radar at Pohnpei, are presented in this paper to further validate this interpretation.