I finally got around to taking some pics of some ergonomic holds to show some personal preferences. I use Bobo's forefinger up approach as I was never able to use the tripod without death gripping (too many years of ballpoint use, and I have larger hands [not humongous but not small]. I've taken 12 pictures and uploaded them. The only way I know how shows the pictures at the end of the post. Apologies for the scaly hands - it is winter here - and other cosmetic defects.
Pictures 1-2 = Wing Sung 6359 (Al Star copy)
Pictures 3-4 = Faber Castell Loom
Pictures 5-6 = Faber Castell E-motion
Pictures 7-10 = Ranga Model 3C
Pictures 11-12 = Wing Sung 698 (Twsbi Eco copy)
Starting with the Wing Sung 6359 photo 1, shows first the pen barrel end resting in the crease between the thumb and index. The pen is long enough to rest comfortably there and at the middle finger distal joint, with a relaxed hand in between. Photo 2 shows that I actually don't use the facets of the trademark Safari grip, and rather rest the index in the middle of the facets. This leads to a wider section, and because the pen is long enough, I can hold it securely at the crease.
The Loom is a similar story. It is long enough. Rests securely. Forefinger up position engages well. The section is more slippery which is a comfort knock on this pen; however I appreciate that this is one of the entry level pens that has a wider section.
The E-motion is actually an exception to the rule. You can tell in picture 6 that the pen lacks a bit of length to rest securely in the crease of the hand, and the small nib also limits the space under the pen for writing at the shallower angle of the forefinger up approach. However, this pen is still very comfortable, in the tripod position, because the section is very meaty, and the pen weight is distributed divinely. This material is also not slippery at all.
The Ranga is the pen in question. What I point out may only be felt by me and the differences are a little subtle. You can see in the first picture that the pen rests in the crease. However the barrel is quite chunky compared to the section that tapers quite dramatically. The minimal diameter of the section is actually quite small. If you compare that to the e-motion section, which is short, the angle is more dramatic on the model 3. That is poor ergonomic design in my opinion.
Compare that the upside down way of holding it. If the pen was designed in reverse way, it would be very secure in the crease, and the section would be chunkier and more secure for forefinger-up position.
I added the Wing Sung 698 because it has a similar quickly tapering section. The barrel is a little less chunky though so it holds more securely at the crease. However, it is not ideal.