It sounds like what you're asking about is a no sparge system. Yes, you'll get the sugars into suspension, but you have to account for the sugar that is locked up in the grain after you drain. Just take an example of a 16lb grain bill. Let's say you went 2.15 qts/lb at 8.5 gallons of water. You'll get about 6.5 gallons of runoff. If you get 70% efficiency, the preboil gravity will be about 1.058. The 2 gallons locked in the grain is also at that same gravity.
You can go slightly thicker at 1.75qts/lb, you'll still be able to recirculate and leave a bit of volume for one sparge. You should get at least another 10% efficiency that way.