I think you're still misunderstanding how it works. XD. Nothing can be above an 18 before modifiers. As you add more points to one stat, the cost to add more increases. So it costs 1 point for an 11, 2 for 12, 3 for 13, 5 for 14, 7 for 15, 10 for 16, 13 for 17, 17 for 18.
Similarly you can...