From the Morphor Dual Envelope's manual, I'm seeing that
1.) There is a length switch on the back of the module to set the overall length of the envelope. Set it to short to get the snappiest possible response.
2.) The output amplitude is 0-5V. This might indeed not be enough to fully open a filter. Do you have a module that can amplify voltage beyond unity gain? Even though some modules are called amplifiers or VCAs, they might not necessarily be able to increase incoming voltage beyond a factor of 1. If you have one, patch the envelope through it and increase the amplitude to try to get a higher voltage swing.
For the Gem LP, there doesn't seem to be a manual available on the web, so I can't say for certain that this is the root cause. You will have to do some additional testing.