Hi Diver Dan
We can and should be somewhat more forceful when sweeping line up into our D loop, if the line being swept is from out of the water, as in the line reversal during a Double spey, Snap tee or Circle cast.
This sensation of extra tension during this line reposition motion can lead many people to naturally get a better feel of control and is largely responsible for them getting to grips quickly with waterbourne Spey casts, as opposed to beginning to master "Kiss and go" casts which require precise set ups and good timing.
I have a point on the Snake roll which I would like to share with you.
I have noticed that the anchors do often have a tendency to drop onto the water vertically rather than sliding in position towards you like on a double spey, all things being equal, the position of the anchor is also roughly vertically below the point where the rod made its "outermost" final turn before going back and up into the D.
The below sequence may help illustrate this.
A line dropping at the anchor end cannot be experiencing the same complete rearward going momentum in the D than a line of the same length which has an anchor point which slides towards you.
If you want the same anchors off a snake as those off your waterbourne casts then the trick is to discover exactly where and just how much effort do you put into D loop formation to ensure that your anchor gets placed in the right position, is completely ironed out straight and under complete tension....
and more importantly, what position do you need to come from so that you can make sure this happens....
I sincerely hope this information is helpful to you.