UGL is attached to RIS on handguard.
But M203, M320(AG36) and GP-25 always installed in a way to be attached to rifle barrel and rests against the barrel-to-body joint, so recoil from shooting UGL is transmitted to whole rifle in efficient way,
G1 grenade launcher (which model has) is used on BREN rifle and attached to RIS, but if we look into manual (https://www.czub.cz/media/attachment/file/i/n/instruction-manual_cz_805_bren_en.pdf page 23 - http://puu.sh/CbHr9/e88896587c.jpg) we can see that rail itself attached directly to barrel.
So current RIS-attached UGL looks unrealistic and should fall off after few shots (or will brake RIS handguard).
It will be very very cool if UGL position can be moved.
Type 1 - is unrealistic too, but little bit more realistic, as UGL attached at whole length. And it should be easy to implement.
Type 2 - bottom RIS should be removed and UGL should stick to barrel. It will be more or less realistic position (it can be moved forward a little bit)