I may have a workaround that might help. Since going from one snapshot to another has an increase in the reverb mix, set up your ambient snapshot with the reverb off and then quickly engage the reverb once you switch over to the ambient snapshot. I realize this requires an extra step but works for me.
I have my patch setup with 4 snapshots on the top row: Clean, Heavy, Clean Boost, Swell. Bottom row is individual effects: Delay Dotted 8th, Dual Delay, and Glitz Reverb. In the Swell snapshot the Glitz is off. I can switch snapshots from Clean Boost to Swell, without the change in volume, and then engage the Glitz effect.