when you have some cash and some of your prices are a bit low (indicated by sell outs) it is easy to optimise your arena by building more seats. this is especially true of the more expensive seats because they fluctuate less than the cheaper ones.
So for your LBs i would build 1 extra a week until you are 1 or 2 seats from selling out.
ive noticed that all my attendances are higher at the end of a season than the beginning and as you can only change prices a few times it can be good to price your cheaper seats a bit high and let the attendance grow to sell out levels.