I thought now that WT+ is between F and J a dedicated c/crew member worked solely in that cabin so the 30 or so WT+ seats is not included in the amount of M seats which I believe in now about 190 seats depending on whether the a/c is a high or medieum J configured a/c.
I presume when it is a high J cabin the WT+ service would be combined with the M service as the cabin would be in front of M.
Some CSD's do work in the M cabin to help out with the meal service but perhaps not on all flights!!!