Even on a LAC border, the “SDCCH mht” will never reach 9.5 seconds. It’s way too much !
Does this cell handle a lot of traffic (TCH) or not ? If yes, then I advise you change the TRX’s or the cell combiner.
If you feel it is not a HW problem, then you can try increasing the Cell Reselection Hysteresis between both LACs, and increase the anti pingpong reselect timer. But in my opinion, you cell has a HW problem. Have you performed a drivetest on it ? what about other QoS indicators ?