so I 'think' I understand what your after the data is a bit mismatched tho. how about this...

a=the number that stretches the parabola. values under 1 flatten it out.

x=your input value 1,2,3,4...

h=the shift of the vertex(ie. lowest or highest point) of the parabola left or right.

k=the shift up or down of the parabola.

so if you want the highest y values at (7,1.267) the h=-7 k=1.267.

now to flatten out the curve to match your data set a=-0.04 or something like that. if your interested in x DOMAIN 2...13. remember the range is y values.

so you get

once you expand and collect you get

does this even remotely help you? fiddle with h,k,a in standard form then expand into general form if you need to. altho your not going to turn a line into a parabola and have your values match up all that well.

if you want something that is linear that goes to a target value then back down linear use a absolute value function

Absolute value - Wikipedia, the free encyclopedia