Presidents Choice Pellet Grills

Hi all….I picked up this PC Pellet Grill (it's a store brand but last year I did some reading and many people felt it was probably made similar to a Pit Boss. There was a sale last week and I was able to get it for the equivalent of $300 CDN so figured it was worth a try. My question is about the second picture….it's not a great picture but the grate above the fire pot has a cover that can cover it or uncover. The manual didn't indicate if this should be open or closed while smoking? Does any one have any idea based on similar types of smokers? I'm use to an offset smoker so they don't have a set up like this. any help would be appreciated. Thanks!