FIA Expansion Tank question, regarding overflow

[Buddy Rawls]

No plans whatsoever to run it dry (not sure where that came from), It is positioned exactly halfway up the highest part of the cooling, there is no way it can run dry if the system is filled properly and it should stay around the 1/2way point. I am talking about the overflow out of the expansion tank (at the radiator cap pressure release port), instead of venting straight to the ground. I may not have been clear enough in the original post. The overflow out of the tank has to be a catch can only (instead of partial filled recovery tank system). if it is a partially filled overflow reservoir, it will keep drawing filling the expansion tank higher and higher (during cooling/contraction cycles), basically negating the expansion tank's purpose.

Two different things in my post.
the Harrison Tank is the expansion tank, it is positioned 1/2 way up to the cooling system components.
The overflow I am talking about is simply to catch and recover overflow, if the expansion tank overflows. It shouldnt do anything when everything is working properly (no blown head gasket etc.)

It makes most sense to simply run the overflow/catch can (under the fender) completely dry. right, as you said. Even if plumbed as a recovery, it will draw back in what it expelled refilling back to the original level. It (the overflow tank, not the Harrison tank) has to be run dry for the Harrison tank to work as intended.