How is Crusade meant to be played?

We started a Crusade, but I have one thing that I cant quite figure out:

With a Crusade usually starting at a 1000p Battle of Order, do you just start playing 1000p games? How do you manage battle sizes if I for example, have expanded my BOO to 1500p but my opponent has 1100p? Do we just do a 1000p game?

Im not quite sure I understand the idea / narrative behind expanding your BOO if you are "stuck" playing 1000p games with you 2200p BOO (just an example) because someone decided not to expand their BOO?

From
One confused Matched Play player