it’s a very common problem.. it has nothing to do with parameters.
It’s just that the TRX that carry the TCH on which you’re going is being transmitted on a different sector. This is a cross-cable situation.
I assume you’re using one X-polar antenna per sector? There are two feeders per X-pol antenna. So if you send the BCCH feeder on the correct sector, but the TCH feeder on another sector, you’re going to experience exactly what you’re seeing now in your drivetest.
That, or the “TCH” TRX is faulty (low TX power). Check the path balance of this TRX to rule that out.