I tend to think the simpler the better and find straight billiards usually the best all around pipe in terms of cool smoking and staying lit for me(everybody's different though) but what is your goal of the vented design? I'm a heating/AC technician by trade(only I deal with bigger pipes), and there are really two roads you could aim for,
1- vented to allow extra draft helping the pipe to stay lit between puffs(which would benefit slow smokers or sippers)
2- venting for heat escape to keep the smoke and the pipe cooler during more intense smoking(which would benefit people who smoke like there's crack at the bottom of the bowl, cigarette refugees usually smoke like theres a prize at the bottom too though(Surprise the prize is tongue bite and wet goo)
Ideally though for vented designs, I think due to the small size of pipes you're really limited in what you can do that will actually function on a noticable level.
also, for the extra draft to stay lit function, you would ideally run small draft holes somewhere that will suck in excess air to aid the combustion of the tobacco, but it would only work for a certain(tiny) portion of the bowl as once its moved above or below the depth of the vents they would no longer serve their purpose, the vents need to be at the point of combustion or the excess air will be of no real use.
and for the 2nd option of keeping the pipe itself cooler you would need to carve a very intricate bowl within a bowl design leaving enough connections to ensure solid strength it's hard to explain what I mean, there are some rediculously stupid pipes on ebay made of steel that convey this principle called "pipe of the future, but I'm thinking more of a brair version of the same principle, I hope you understand I'm confusing myself trying to explain it.
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Also I may be wrong as what I've said is just my opinion, I usually work with residential, and industrial heating and cooling systems but the principles of combustion and heat dissipation should also apply to pipes though the sizes and the way pipes work is very small and restrictive draft wise, there is only so much that can truly be accomplished in such a limited space.
But as usual I've been into the whisky again and don't know how much sense this all makes, if its confusing I could draw pictures(limited to stickmen and basic shapes)