At the moment there are only 2 settings for the cycling envelope for rise and fall: linear and percussive. It would make sense to have a third option or a seamless transition from logarithmic to linear to exponential, or vice versa, depending on whether it is a rise or fall.
If, for example, you want to use the cyclic envelope to make the pitch fall SLOWLY after releasing the key (Cyclic Envelope → Pitch 12 and Osc1+2 -12 semitones down), it quickly becomes clear that even the highest value of 100 for Fall is still too fast. Here (and certainly in hundreds of other cases) a logarithmic progression would provide a remedy.
To do this, the Shift+Rise/Fall behaviour would simply have to be supplemented by another curve and the middle (value 50 and ONLY the value 50) would mean a linear progression of the curve.