The Roland 100M dual VCA works a bit like the ARP 2600 VCA: you have to raise the initial level slightly before it'll be reactive with the EG's output. But keep in mind that once you've got that slight "open-up" set, you'll need to really "thump" it with the EG's output into one of the VCA slider inputs. Also, try switching between LIN and EXP to see if things improve; linear response is what you'd normally use for CV and modulation signals, and the exponential response is tailored for audio use.