an ARFCN defines both an UL frequency and a DL frequency.
If you assign ARFCN=1 for a BCCH, it means the TRX tx@935.2MHz and the MS tx@890.2MHz.
So both DL and UL should be interfered. And the UL will be more interfered because the MS are spread over a large area, resulting in multiple sources of interferences for the receiving side (the BTS)
On the other hand, in DL, the MS are usually more concentrated around their cell, and quite fare from the intereferer cell.
regards
pix