Hi,
for this, you make one curve that starts at 0 and end at 1.
then you multiply the result of the curve animation to range from 0 to x, x being your multiplier. Else you can use "FloatRemap" on the Ecosystem for a more complex mapping of the value.
So this is a two step thing, animate your normalized curve and then stretch it's range before using it to control your targeted Property.
Hopefully I understood properly your issue, else let me know
Bye,
Jean