Fishingsurveyor: You are doing fine . It is possible that wind blowing or current can make the ice move up and down slightly which in turn will show your bottom changing [up and down ] hence the flicker. I notice this some times when a snowmobile passes by close and the water in the hole sloshes around , the bottom flickers more for a moment.
Also I believe , if you have zoom on - the sfl goes on automatic.
Good luck with your Marcum you will love it I'm sure... Wiz