John: It is hard to see anything in that picture. But, yes, it is fairly common for the front edge of the cook box to bow out on these grills. You are very lucky that you got the Honsgo version of grates because they are slightly longer than most of the other SS solid rod grates out there. I have had some where the grates very nearly were falling in off the ledge when using the other grates when the box was bowed out a bit.
If you look down the top edge of the front of the cook box from side to side, you will be able to see the bowing in the cook box.