Rapid rooters dumb ass question

Ok I know this should be easy and straight forward but here it is. I’m getting ready to germinate for first time using rapid rooters. I have the 50 plug tray but only doing 5-6 at a time. If using the tray for only 5 plugs how much water do I add to the tray. It says a 1/4” but that seems a lot for small amount but don’t want to worry about to much. I can’t seem to come up with a alternative or find any info on this question. Any help would be welcomed. Thanks

I'm not a fan of germinating out of whatever medium I'm using, so I really don't use the rapid rooters BUT there's a video from Welcome To The Growtent germination video where he talks alot about this. I'd skip the plugs, but if you really want to, watch his video. Don't listen to his other advice though, YouTube growers are poopy lol.