I don't know if I understood correctly, I use VMWare Player, and normally I use 1024x768 settings, now for testing I modicated the resolution in GRUB to 1280x1024 permanently and everything worked, these are the affected items I midified
# Set default boot entry as VESA Gfx @ 1280x1024-32bpp
set default=4
}
menuentry "AROS (true colour VESA graphics: 1280x1024)" {
multiboot /Arch/pc/bootstrap.gz vesa=1280x1024 ATA=32bit nomonitors
I forgot, the VM must also be set to 1280x1024, or use the option "Use host setting for Monitors"