The reverse sear is a wonderful technique to use for any large cut of meat whether it be beef, pork, lamb or even chicken. The concept is simple. You slowly raise the internal temperature of the meat while introducing some smoke flavor (if you choose to do so). Once you are within a few degrees of your target internal temperature you crank the heat up and finish off with a final sear. By allowing the internal temperature to slowly rise within the meat you end up with beautifully cooked protein that is one solid level of doneness throughout. If you try to cook a large piece of meat on your grill right from refrigeration it will have the five seasons of doneness. Rare in the center, a medium rare ring, a medium ring, a gray medium well ring and finally a dryed out flavorless outside ring.

There is an easy way to take this up a notch further. Use the GrillGrate with the flat side up as a plancha and you can get a better Maillard reaction on the meat.
And, per testing reported by Serious Eats and others, letting a piece of beef sit at room temperature doesn’t do much, you can cook it right out of the refrigerator.
Finally, reverse sear is probably the best way to cook a steak that is at least 1.5- inches thick.
We concur!
I do not understand how you are using the flat grill side. Is it for the searing finish or for the “baking” part of cooking the meat?
We are actually not using the flat side in this particular technique. However, as Robert Points out below, when you go back to do your final sear, you could use the flat side just to get a little more sear/char/crust than the rail side.