Puzzdre..... DAMN.... you are getting good at this! See, I told ya so.... not too hard at all.
Structural integrity as well as heat transfer, you guys are both correct yes. the two plates get bolted together really hard, with 4 SS bolts so as far as the heat is concerned, it's pretty much one continues pin, all the way to the top. which, if one side is drilled 4mm, would mean the pin to be 8mm long..... now that is a mighty long way for heat to travel, when you consider the environment that pin finds itself in... just think of all the miniature little vortices and turbulence, and it changes with the smallest rise or fall of fluid velocity.