Help making scatter with stright lines end point at X before line end

Chart data:

....................Point Blank..........Optimal.................Falloff...................2xFalloff
(X)Range Km.......0......................55.......................93.........................131
(Y)% Chance......0.723913238......0.723913238........0.361956619............0

Ok so i will always have a flat line and from optimal to 2xFalloff but there is just a point in the middle called Falloff marking out the half chance.
Now what i want to do is have an x value that no matter what the chart just stops graphing that one line at X because the data above is just one of 4 lines in the graph

the graph has to keep the y range of 0%-100% and an X range of 0km-249km
so I'm really just trying to end each individual lines X value at a certain point before 2xfalloff
will i have to make a formula to calculate where in the line it would be and have a check that checks to see if it would even be in the line?

For Example:
to the graph above i would like to have a forumla so that if i enter 97.75km in a box it ends the cirten line there that would be a little past falloff (the half way point)
The chart type is Scatter with straight lines

I would imagine most don't understand what you are asking, I don't.

maybe you could post example workbook illustrating what you are expecting.

Still not sure I understand.

I've inserted a new column to calculate value between points.

nope, don't understand and your explanation is not making it any clearer.

Maybe somebody can dechiper what it is you need.

you can't do that. You have to change point B to be the new terminating value, what ever that is.

You can have original point B displayed in the table just don't give it a Y value and the line will not be drawn