The distance between the bearings need to be same from the center of the bit. This will give a true cutting. Pending on if you're pushing or pulling the router, also depends on which side each bearing rides on. You still need to have a certain amount of room for glue up. You make the mortises first, then the tenons. The tenons are made to fit. Check your measurements from bearing to bit. If these aren't the same, your mortises will be off.
I have the OP 7" x 7" plate and the bearings are dead on. Makes mortises quite easily.
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