I spoke to a mechanic at Capital Moto in Clapham (where I bought my bike) who suggested that I speak to Bike Trac before trying any other solutions.
He explained that when the Bike Track doesn’t have signal it will try extra hard for a short period of time to find some signal, thus making draining worse when you bike is underground.
Just got off the phone with Bike Trac who confirmed this and tweaked some settings.
We’ll see what happens!
@Jay still see your very valid point about not having signal on the bike while its parked, but sadly I don’t see a way I can boost that signal down there.