The answer to your first 2 questions is yes, both will narrow your gaps as will a heavier/slower arrow...
I shoot 3 under with a medium to high anchor and with a 50lb bow my point on is 30yds. I also shooot arrows about 4 inches longer than I need..
I'm not a dedicated gapper, but I still like having the small gaps.
I'm not quite sure I follow your last question, but I would assume if you change the left/right portion of your anchor, your arrows will react as well. However, you can play around with your shelf material to offset it.