The NoL sets would have been going through the Channel Tunnel in pairs, not as standalone units, which would have meant that they would be no different in size then to the full size 373 units.
You see what would have happened is a set from Glasgow/Edingburgh would have joined up with a set from say Manchester at somewhere like Ebbsfleet say joined together and then gone on from there coupled together.
Wow, no, you've imagined all of that. That's quite some fantasy. The reality is that they were designed to operate solo, with the same ability to split in the middle as the Three Capitals sets, just with four less carriages so they could fit into (some) domestic platforms.