In case your RACH is low, can you please share if the cell has got Excessive TA drops? Is MAXTA reduced on this cell? Because one reason for RACH failure is due to the detection of excessive timing advance in a RACH access burst which will be rejected and counted as failure.
Also, when checking for BCCH/BSIC combinations, make sure you are concentrating on the BCC Part of the BSIC. because it might be that two co-BCC / BCCH cells are located in near vicinity creating high RACH failures.