I never even thought about this. I like my subs to have a very short attack and a little bit of a release time, such as you'd hear out of a bass guitar. This is completely independent of whatever envelope I am using on my main bass. I think you may be overthinking it. Hardly anyone can hear the attack or release of a sub. That's what the main bass is for, anyway.
Oh! This does make a massive diff to my approach then - I thought they had to sync perfectly. Thanks - this is pretty vital info.
Then what about legato - do you have a sub bass to start the envelope again on every note, or do you want smooth legato. Same with pitchbends? But - yeah - if what youre saying is standard practice to have them slightly independant then I guess it doesnt make that much diff.