How wide is the un-mowed strip?
Because your mower has its two blades driven by a conventional V belt, not a toothed belt, the blades are not timed relative to each other. Hence they cannot overlap, or they would strike each other. They also are not staggered (one cutter slightly in front of the other) so they could both be brought closer to the centerline of the machine. It follows that the only way to minimise the strip that is not mowed, is to always have new blades on the machine: any tip wear whatever, leaves the blades clearing each other by a larger amount, and leaving a wider unmowed strip.
I suggest you look at the blades from underneath - WITH SPARK PLUG DISCONNECTED OF COURSE - and see how much clearance there is between them when you align them so that their tips are as close to each other as possible in the center. I think you will find the clearance is exactly the width of your unmowed strip. Then measure the length of each blade, and compare that with shiny new, genuine ones.
