An idea of tail expansion heat pipe is introduced for heat pipe application.
On the evaporator area, an expanded diameter design benefits the conducting area with powdered wick structure inside of the heat-pipe, carrying more energy through phase changed vapor.

The other side of the tube is considered as condenser side. A smaller diameter tube allows smaller bending radius, and brings in a better space arrangement of heat-pipes line-up.

Below is the performance chart for comparison.

An dual diameter heat-pipe is expanded from 6mm to 8mm. Its performance line is marked with green triangle.
The expansion gives the dual-diameter heatpipe a close performance as 8mm diameter heat-pipe. And its advantage is shown on price, performance and bending space.

Performance Comparison
A previous Cooler Master retail heatsink has four 6mm heat-pipes on the module. Cooler Master modified the design, and latest proposal is a module with 3 dual diameter heatpipes. Those two modules have the same performance but the latest proposal will lower the cost. 

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