VXA-2 tape really full ?

I am backing up several PCs using Backup Exec for Workstations
(version 4.61) to an Exabyte VXA-2 tape. I just started getting
the message that the tape is full and it wants me to insert another
tape. In theory, this is an 80 GB tape drive and I am using the
VXA-2 80GB tape. This problem started happening using
hardware compression and continues to happen using software
compression.

Backup Exec says that the tape is full at 1,683,781 files with
102,255,765,292 bytes with 1.89 : 1 software compression.

I am totally surprised that I cannot write at least 150 Gb to the
tape. Is the 64K block size on the tape killing me ? I did erase
the tape using Exabyte's vaxtool first.

Is there some method of telling me exactly how much of the tape
that Backup Exec is using ?

Thanks,
Lynn McGuire