The Editor preferences where you set the starting resolution for standalone game will ignore the values given if they exceed a certain amount. In my case 1920 x 1080 was the limit where it started to ignore the values.
If you use the console variable "r.setres" it will change the window size to values that the editor preference couldn't accept.
The window will default to 1600 x 1000
The window appears at the specified resolution even if it is larger than the viewport. This is how the console var "r.setres" works.
Head over to the existing Questions & Answers thread and let us know what's up.