Without the flattener you will be using the ‘standard’ scope specs - which is the overall 840mm. It’s slightly confusing because (I think) the 225mm refers to what is available, not (just) what is required. So for example, you could construct an optical chain with Barlow, adapters, filter wheel, diagonal etc. which is longer than 225mm and this would not be able to reach focus (because it’s too long). So as long as you are imaging with an optical chain of less than 225mm, you will be able to reach focus (I.e. imaging plane is at 840mm) using the supplied focuser.
I hope that makes sense, I’ve had a very nice beer or two now.