Connecting Expansion bottle

[Numplumb]

Where are people who are building MX5 builds connecting their expansion bottle to?.
I have a VW Polo rad and expansion bottle also from a Polo, do I tee it into the top radiator pipe or could I connect it to the redundant connection at the rear where the heater was and blank off the pipe going to the water pump along the side of the engine under the exhaust manifold or anyone got any info how they have done it.

Regards Mick.