damping line output

Hello,
I'm trying to modify the output of a slider depending on the distance of values in a time window. If the difference is bigger, the time to that that value should take longer. In the example this is happening already, but I would like to "damp" the time if the target value is nearing. The 5th exponent parameter in [line] does the opposite, by going faster at the end.

Thanks for any ideas
Frans-Jan