The issue really I think is that Hype is document based.
So if you open a doc from someone else or have many docs open and some different sizes.
The task is to know which one should be the next default size. Which I would avoid trying to do which I think may be the case of why we have what we have.
But a better solution would be to have an option to save any open Docs size/position as a default.
This would then be the default for any new Doc window.
You could also have a menu item to set the current window to the default size.
And you could also not only have the save default option but save as a named size, so you could then change your default to a named one and also be able to switch at will to other set sizes.
I know this works because I use the app Media Pro that does this. It is a Document based app and it works very, very well as described.