Setting output size in Articulate Replay?

Hi all,

Apologies if this has been asked before - I've searched but I can't find anything. I'm trying to make some short training videos which are basically just screen captures of me using a piece of software and talking over it. One of the pieces of software is for mobile devices. I'm 'faking it' by running it on my PC and resizing the window to approximate a phone screen - but the video output from Replay is coming out at 900x1200, even though I was recording a 900x500 window. This video is intended to be watched on a phone, so with the extra sidebars it's making the actual content too small to view easily.

Any ideas? Thanks in advance.