Well it shouldn't matter what the buyin is regarding trying to play each hand as well as possible. If you are having trouble maintaining focus in the lower ones that's probably not much of a problem. I can't imagine anyone decent having a true ROI of less than 50-100% in the big field $11s (although being such +EV games they are still a big gamble on variance if you look at a simulator). So if you aren't paying much attention to the game you probably aren't giving up a huge % of your edge? I could be wrong about this but the logic makes sense to me. If you get into a big pot and aren't sure what to do you can always time bank, open up the replayer, and see what villain has done in showdown pots if you have no idea.

Regarding focus I will share what works for me and maybe it will help.

Rather than try to focus on every game equally I will adjust the tables are on screen so that the one I to follow action on the most is in the center and put the other games in corners. Typically this will be the lower buyins, in corners and highest in middle - though you may have a low buyin in the middle if its late in the tournament or the bubble of a satellite will need the most attention. It should shift depending on the stage and doesn't correlate to buy-in size, though as a default if all tournaments for the day started at once the smaller field combined with larger buy in amount would be centered, with bigger fields off to the corners.