IIRC, The CV64/3D should map into your FAST mem area on a stock A4000. So, if you have 16MB Fast, 2MB Chip, and a 4MB CV64/3D, when you boot, you should have....
~2MB Chip
~12MB Fast
4MB missing (not listed in avail, but reserved for the CV64/3D)
If this isn't the case for your system, you might want to see if a jumper is mis-set on your CV64/3D.