If you want the 'value' at level 25 to be higher than what you can get with the curve generator, you'll have to set each level manually.
Use your Right Mouse Button to view/find level 25 on the curve chart. Use the Left Mouse Button to set (drag) the value to what you want.
From that point you can hold the Left Mouse Button and 'draw' the curve between level 1 & 25. (it takes a steady hand & some practice.)
If you want your curve to follow a specific mathematical function (linear, parabolic, hyperbolic), you'll have to set each value manually.