I catch stuff out of my peripherals quite often as well, lol then I concentrate more on trying to avoid looking than what I'm aiming at. I'm more used to 2 lane courtesy, so I generally give it, most people I bowl with do even if it's not a league/tournament rule, but if I'm only getting one lane or if people are standing up on the approach waiting, I'll take extra time toweling the ball off, examine something on my shoe, etc., until they go ahead and go. I've made a lot of progress with just getting up there and going, because being easily distracted feels like a mental game weakness. But honestly, if something out of the corner of your eye breaks your concentration, sometimes it's tough for even the best bowlers on the planet to refocus without stepping off or resetting. Maybe a little over sensitive, but it doesn't sound excessive to me.