I haven't used this myself so I might be wrong, but:
The sprite pattern table select bit in $2000 has no effect on 8x16 sprites. If you have an 8x16 sprite and the tile index # (call it X) is even, you take tiles X and X+1 out of the $0000 pattern table. If the index # is odd, you take tiles X-1 and X from the $1000 pattern table.

So if the tile index # is $FF, you take tiles $FE and $FF from the $1000 pattern table.

Hope that helps.

Abonetochew