If the chain is new/newer then I would definitely adjust it as needed. I ran -1 front constantly on my 600RR, but could run anywhere from 42-45t rears (0 to +3) with the chain ending up the "ok" adjustment area. As for the -1/+2 thought, that equates to about a +1 in the rear overall which would move the axle adjuster slightly forward, not backwards. Bigger tooth rear sprockets increase's size and brings the rear wheel forwards to the front making a shorter wheelbase. It's a give and take when only using one chain with different sprockets to end up with what you want. (be it accelerations, speed or wheelbase etc)