From the observation that many channelers, like Rand & LTT, but also Demandred or Rahvin, are similarly very tall. It also seems that Lanfear is the only Forsaken, who got a much smaller body than her previous one (e.g. Ishy even got a bigger one). If e.g. Lanfear's soul can't completely unfold her whole OP potential in Cyndane's small body, this might explain her strength drop. It makes also sense that this relation between soul and body concerning the OP strength might be a detail, which was somewhat hidden in RJ's notes.

At least this is the only main remaining theory on Cyndane's weakened strength, IIRC.