Every level has a cap. of maximum capacity
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There is a Little trick to have a idea of the Best price, set the price to maximum, then divide that number by 4 and you have the ticket price.
For exemple If the maximum price is 20, the good price is 5.
For CL and CUP put the price 1$ higher that in LEAGUE.

Depending of your results, you can try put it 1 or 2$ higher.
Of course If you put the price 4$ higher you Will not have full stadium! but Will gain more money, because of the diference in price.