Well, as I said, my aim in alternating the grip is basically to work on my full shaft, only with more emphasis on the upper half of the shaft, since mine is larger at the base (quite larger in fact, if you look at my stats).
So, the first 500 jelqs I get a mix between both grips so as to work on my entire length. On the second set of 500 I use only the standard OK grip so as to NOT work on the base and focus mainly on the rest of the shaft, to see if I can even the girth a bit more

I haven't done any kind of experience with angles for any significant amount of time, as I do my jelqs horizontally, both with the standard grip and the overhand grip. However, I've tried jelqing with the overhand grip, at about 80% erect, and, if I point my penis down, the rush of blood to the glans is huge. You can really feel it engorge as you jelq down the shaft

However, since I jelq sitting, it's not very comfortable to do this. It works better if you do it standing.
Oh, one more thing I've added recently. After I finish the 1000 jelqs I then do the following:
- do 1 jelq until halfway down my shaft and then hold the grip for 10 seconds;
- change hand and do the same, starting at the base, jelqing until halfway down the shaft and holding the grip for 10 seconds.
I do this for 10 repetitions (adding up to 100 seconds). The aim here is to focus on engorging my glans with blood, so I can get that nice mushroom head.
Maybe it is just my imagination, but after only 2 days of doing this, I felt like my glans was already larger when erect rofl