I have had this problem for a long time: when I open a worksheet, made with a PC with a resolution of 1900x1080, with another pc with a video resolution of 1600 x 900, the layout is completely messed up. Is it possible, instead, an automatic adjustment of the page when passing the file from one pc to another? In the image what actually happens.
One thing you may try is from the menu item File | Page Setup use a size of 800x600 (SVGA) on both computers to get an 800 pixel wide page.
The procedure, recommended by you and which I have not yet applied, is feasible, I suppose, only with new worksheets, instead with those already realized and of large dimensions it is not.
I wonder what type of printer you have selected that allows you to choose a paper size of 'Screen 800x600 (VGA)'. Or is this only possible with Mathcad 15?