I did some searching and found where Peter with hand size M/L used Lamkin Midsize Crosslines with considerable build up, using drywall mesh tape. Resulting in 1.06" diameter at 2" from the end.
And a couple of others recommending .580 core grips, which are slightly oversize, then a number of wraps of build up tape under each hand, varying according to hand size. For instance, I wear a M glove, and the chart showed 3 wraps lower, 1 wrap upper, with the .580.
Right now I'm using a standard .600 core grip (Tour Velvet) with no buildup under the upper hand, and 4 wraps under the lower hand. That keeps the upper diameter at .915 at 2", and the 5" measurement is about .850. This was the result of trial and error with my old method of holding the club, which I now have determined to be wrong. My lower hand hold has not changed, but the upper hand has. Now I'm holding it properly for IMA, a bit more up in the palm than before.
My upper hand hold doesn't quite feel solid now. The gap seems to be in the middle of the upper hand area, especially where the ring finger meets the palm. I think I might need a larger diameter in the upper hand. Is that likely the case? I ask because it might just be a matter of getting comfy with the new hold.
The proper grip size under the lead hand is a grip size that will let you swing into high grass and not have the club rotate in your hand (with a tight grip of course). There is no official guidance about the trail hand grip size. Given the action of the trail hand there is no necessity for build up there. I do my buildup under the entire grip just to insure no lumps or sudden drops.
Larger grips would still not be large enough so I'd have to add buildup. Also the difference between a large grip and the standard grip I use is minimal in terms of the number of layers of buildup so I'd save very little. Given this and the fact that I much prefer the feel of the Lamkin Crosslines vs the oversize grips I've tried makes it an easy decision.
BTW - single diameter grips like those from NG and others leave the diameter under my lead hand too small. Because the grip cap on these grips is also apx 0.9" they wind up with a 'bulge' at the cap when you add significant build up. Regular grips have a much larger cap diameter.
The reason I asked is that there is a Crossline Jumbo (+1/8") versus the Midsize (+1/16") that you are using. It weighs 10g more than the Midsize. Without buildup it should be in the area of 1.025" at 2", pretty close to what you have.
I don't think that was available when I switched to the Crossline (I looked for the largest Crossline available) but I'm pretty certain that it would still need buildup as I've worked with other grips that are 1/8" oversized.
Aren't these the old, original NG grips? Edwin Watts used to carry these where I live and I used to buy them there when I started working with NG. They haven't carried these grips for a number of years now, though. I never really cared much for them. A personal thing, I guess, just never had a good, tacky feel to me but frankly the grips that NG replaced them with didn't either imo. I did like the "All Weather" grips they came out with but they needed a bit of build up.