Hi Jack,
Since problem is clear with only Sector A’s incoming HSR, there must be issue with sector A, be it radio or paramteric.
Check BCCH and BSIC/BCCH combo for A, it should be clean in the area.
CHeck Interference in the area as you said cells around A r also affected.
Also how is the situation for B–>C ?
Rgrds.
Optim