The shorter you bring it in, the more extreme the 'X' becomes once you're shooting past convergence. The way I tend to look at it is whatever my convergence is set to, my reasonable range is about double that. If you were to draw the bullets as a straight line, and your convergence is 300, your bullets would be the same width as they are at 0 out at 600, still a reasonable concentration of fire to put both streams on one plane or one bomber wing. Now obviously that's not exactly true, because of dispersion, at 600 the rounds spread quite a bit. I still find I can do damage to a non-maneuvering opponent at that range.
If you start bringing it in closer, say to 200, now your bullets are the same width they are at 0 at 400 yards, and you're only going to be able to put part of the fire from one bank of guns on the guy at 600. The X is too fat, and it moves the second bank of guns' fire off too far to the side.
Now, looking at ranges closer to either side of convergence, with my convergence at 300 I generally find hitting at about 200-400 gives me an excellent volume of fire on the part I'm aiming at, little different from hitting him right at 300. That gives me basically a 200 yard band where my damage is excellent. If I move my convergence in to 200, my bullets are the same width at around 275 and 125, which means I've only got about 150 yards putting the same volume of fire in the same area.
TL;DR: If you shorten it up too much, IMO it shortens up the range where you can get acceptable volume of fire on a plane, and shortens the range you can ping for damage, not just to make noise.
I like the versatility 300 gives me, even though I do most of my shooting inside 300. I don't think the gain of shortening it up outweighs the loss in versatility.
Wiley.