Hmmm...
Of course, on shrouded connectors the end doesn't make contact at all; it's a plastic insulator... but your point about them not appearing very long is valid. A little calculation with a pair of dividers indicates the radial spring portion is approximately 12mm long, which means optimum contact area is at ~4-8mm depth or so.
I also am a bit annoyed at not getting green with my cable set... though I can pretty easily buy a couple meters of green silicone wire from Banggood to go with my ends.
Dammit... 
mnem
Fuck Chinese cabling for now; there's Chinese FOOD calling my name.
Even on none shrouded ones where the end is not insulated, it
still does not make contact as the dia is way less than 4mm, about 3.6mm so the onlu connection being made is the bulbous part as mentioned before, the Pomona ones do not have the smaller tip, the ballon or bulbous section starts right at the very tip of the plug as does the ones I have selected, picture below.
Yes there is a small tip on those as well but then the 6 individual springs along the side of the shaft are widest just behind the small tip and they have a total length of 22mm of insertable plug before hitting the insulation of the body whereas the ones that I think you have ordered and I previously ordered that total length is only 15mm and the length of the smaller non contacting tip, from the tip to the start of the bulbous section is 5mm, which means at least 7mm of the bulbous section of the ones I picture below is actually in the input socket of the device being connected. I love this type and have had zero problems so far.
@bd139, do you know how long the insertable section of the Pomona one is at all?