Since Malayoid was a none flyer it is possible that the tail became modified to better serve a different purpose such as shedding rain water and enclosing the back end from where the vulture hocks leave off. Needless to say it was probably carried low. Even flighted Jungle Fowl will lower their tails in the rain.
This bird which I've posted before has flat vaned rectrices like the Jungle Fowl, but I discovered in the Cochin Bantam, or Pekin as in is known in Great Britain, some that have rectrices that could not be distinguished from the surrounding curved contour feathers that fit so smoothly around the body. Now the Cochin is from China and probably a very ancient form having been "found" in Peking as well as in Shanghai. This is intriguing as a tail made up of contour feathers would make a very nice fit with the similarly curved vulture hocks above.
If the abdomen or "fluff" as it is known by fanciers were reduced and the very full feathering, this type of tail feather would blend well with the hock feathers creating a smooth contour for a bird that never left the ground.
This contour tail does not appear to be an all or nothing trait. It varies by degrees from short rectrices in the American breeds derived in part from the Cochin, Rocks, Reds, Wyandottes and the like, to the completely morphed tail bun of the Pekin.