I had the same issue last season. If you look at the attendance helper, the line that it draws through the data is the average of each seat price. Then it draws a line through the curve at the number of seats that you have. So what it is doing is telling you what price to set for the average team. Now you just promoted so right now your attendance is way above average so I would use that price you get from the attendance helper and add probably about 10-20% to the price.
Also your arena is a little small, so i don't think you will have to worry about not selling out. It looks like you may need to lower the courtside seats a little since you aren't selling those out.
Keep building you always need money.