Don’t know if this helps, but if you mean the big metal plate thing like in this picture then it slides right up to meet the back wall of the wood burner. But, as you can see, there are holes on each side (the triangular section), but which doesn’t allow the flame to directly reach the flue.
https://picasaweb.google.com/lh/photo/3ILs65e6cEvNXlKbxgQsnzvT4XCVrRobvmJ9K-DerAE?feat=directlink
Doing a quick google, it looks as though there would NOT normally be a gap. I read one report saying the baffle plate had slipped out of position and this had allowed the flame to directly heat up (massively) the flue, which caused a fire. I think the idea is that the baffle stops the direct flame and heat disappearing up the chimney/flue, plus it creates that swirling flame effect (looks nice) and in some cases, it might be used to help with airwash for the glass.
Having said all that, I reckon fitting the baffle plate, and the design of the baffle plate, varies from wood burner to wood burner, so I guess you really need to seek out some advice from the manufacturer. Unless its homemade, you should find the manual on the web, no ?
What make is it ?