The sprout ratio I think depends more on the seeds. I have some wheat feed from last year that less than half will sprout. The fresh seeds from Power Grow all sprout. The covers seem to keep more moisture in. The sides of the containers are clear so they are not really in the dark.
Just took a close up look at the wheat grass seeds that soaked 12 hours yesterday from 5:30am to 5:30pm and all of the seeds have started to sprout at the 24 hour mark.
I have 5 pounds of barley on the way to test with as I've read on here many times folks sprouting barley seeds for their chickens.
JT
The lentils I sprouted did great. The last batch of organic 3 grain scratch about 50% sprouted. This new batch I left covered longer and it did considerably better. I am also working on sprouting flax seed for them (I had a bag we aren't going to eat) and that is going well. I am following this technique.