Help with external hardware routing

I’m new(ish) to Cubase and I’m hooking up external gear for the first time and want to make sure I’m doing it correctly.

All of my tracks go to a Submix (kinda like a VCA but used for processing) and the Submix goes directly to my main Stereo Outs (no processing).

I have the External FX setup and am getting signal to my external HW compressor. The question I have - should the External Plugin be used as an insert on my Submix channel or on the main stereo out? I currently have it inserted in the POST fader slot on my Submix channel.

Also does it matter if the External plugin is pre or post?

Hope this makes sense and thanks for any help.