This cocciopesto floor appears to be in phase with the opus reticulatum walls in room G-14, and therefore also the section of mosaic seen in the northeast corner underneath wall 6132. The eastern limit appears to have been cut, but is more likely purposefully constructed to occupy half the room with the other half covered by (now gone) mosaic.
SU 6146. Photo taken from the east.
SU 6142. Photo taken from the east.
Room G-14 floor
Photo from east