The amount of flavor you get out of the grains depends on the water getting to the center of the kernel and leaching the flavors back out. They have to be crushed well to get that water in. Another factor is how compacted the crushed grains are when steeping. The muslin bags seem to be pretty tight. I'd go with a nylon paint strainer bag for steeping now that I have learned about them instead of the muslin bags.
Now that you have the Corona mill and I've mentioned the paint strainer bags, you might want to consider going all grain BIAB. It doesn't take much more time than extract with steeping grains and the most difficult part is getting the temperature right for mashing.