Adjusting formulas to accommodate variable size of input data

Attached is a file where I need to change a given shape based on certain parameters.

The input data shall be copied from another software to columns A and B below row 10

Based on values from C1 to C6 a new shape has to be generated. (C1 and C2 shall be manually entered)
The formulas for the new shape is entered in columns D and E. Presently only column D changes.

The problem is that the size of the input data varies and so does the location of '0' and the formulas depend on the position of zero. (I have provided a second set of data for checking purposes in columns A and B)

I would like to modify the formulas so that the shape is correctly modified. This shape modification can be visualised by changing the values in C1 and C2 as suggested in the file.

For the current values & formulas, i have attached the modified formulas.
There is a Helper Column which i have used for getting the desired results.
For the getting the correct value in C4, below formula is used:
=INDEX($B$11:$B$24,MATCH(0,$A$11:$A$24,0)-2)-INDEX($B$11:$B$24,MATCH(0,$A$11:$A$24,0)-1)

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Thanks, Tils. Yes this is how I want it done but you have missed out the effect of C1. This is supposed to change the slopes next to the bottom horizontal line.

Frankly speaking, i didn't understand exactly what you are trying to say, but i found out one mistake in my formula which i have corrected. Below is the formula to be used in cell D11 and to be dragged down:
=IF(ABS(F11)<2,A11,IF(F11=-2,D12-(E11-E12)*$C$1,IF(F11=2,D10+(E11-E10)*$C$1,IF(F11=-3,D12-$C$3,IF(F11=3,D10+$C$3,IF(F11<0,D12+(A11-A12),D10+(A11-A10)))))))

Actually I was looking for something more flexible so that the users do not have to worry about deleting or adding lines at the bottom of the column. I am not worried about #N/A values but the graph should be adaptable.

Thanks. Actually this data has been imported from autocad manually and has to be returned to autocad after the modification.

I shall now write a routine to automate the import and export. Unfortunately the CAD topic area is not so active otherwise I would have posted this part there and someone could have had a chance to bag a few points.

Shape-modifier.xlsx