need help changing block size on lto4 tape drive

Running dp 6.2.

The tape is connected to a scsi port on a windows server running r2 2008.

The cell is on another windows server. 

I am unable to change the block size for the lto4 tape to anything other than 64M.

Is this a windows limitation? I tried to disable to windows driver for the device, but then DP can't write

to it at all. Any suggestions?