I’m noticing that, when sliding up to a note (which I love doing) it’s far easier on a soprano D than on a Low D, despite the larger holes of the Low D. The reason is that with piper’s grip, the fingers over the 1st, 2nd, 4th and 5th holes can’t slide forward over the hole very much. Do people particular sliding techniques with Low D whistles that make it work better?
Mike, you bring up these questions that always make me stop and think about how I play. And I really do not think about how I play very much. 
And I guess never really thought that the EZ grip presented any limitations on playing. I am far from dogmatic about playing techniques. I believe in the “whatever works for you” technique.
So having stopped and looked at what I do since you asked, here’s the short description. With the two ring fingers I tend to slide them on and off of their holes sideways. The index and middle fingers tend to slide off the holes from top towards the bottom of the tube going up a tone or sliding from bottom to top when going down a tone. I also tend to lift the top finger off the TH1 hole from side to side quite a bit going from b to cnat to c# or back down from c# to b. But there are other exceptions which seem to be more situational, particularly for half-holed notes. Depends on where the fingers happen to be at the moment and what has to happen next I suppose.
Again, I don’t think about what I am doing but more about how things sound. The fingers kind of do what it takes to sound the way I want things to sound.
Feadoggie
Maybe I think too much about my playing but even after two years playing the Low D (and high) I seem to be very much a beginner with lots of questions . . . at least in my eyes anyway. It seems like a long journey! Thanks for your thoughts though which make a lot of sense. If you can’t move side to side then up and down is fairly logical! I’ll have to experiment.
i think of sliding on low whistles (piper’s grip) as rolling my fingers back, or up and away from the whistle. so if my right hand is on bottom, and i am sliding from a low D to a low E, i’ll roll my ring finger forward from where i’m sitting, up and away from the whistle.
i imagine this is what you were describing as well.
I have no problem with sliding from D to E, or from G to A for that matter. In both cases I’m starting with the end of the ring finger over the hole and therefore sliding as I would on a high whistle. It the other fingers/holes I have the problem with where only marginal forward movement of the finger is possible. But Feadoggie has described well how he deals with those situations.