So you wanna start VaM windowed and lower than 1080p. Did you try creating/editing batch file with custom res?
1. Create a copy of VaM (Desktop Mode).bat
2. Edit it with notepad (or similar text editor)
3. Set desired resolution and windowed ( -screen-fullscreen 0
, otherwise "1" or -window full
)
for example: START "VaM" VaM.exe -vrmode None -screen-fullscreen 0 -screen-width 1280 -screen-height 720
4. Use it to open VaM, don't start VaM via VaM_Updater (launcher) or VaM (Config).bat