Has anybody put their temperature sender on the plug underneath the thermostat housing? I currently run mine out of the top plug, but am unsure of how accurate it really is b/c of possible air bubbles up there when it gets hot...would the plug on the side of the block still be a good 'high flow' spot?

 

With normal system operation, any air (or other gases be they free or dissolved) trapped in the coolant system is expelled to the reservoir. Plumbed as such, the reservoir replaces that air with coolant.

The reason behind the design is that eliminating any oxygen in the coolant circuit, greatly diminishes system corrosion.

Ensuring your system works correctly will eliminate any concerns with bubbles.