Proportionally splitting a value between cells based on values and conditions

[Midavalo]

In my data I have a couple of columns that are added to regularly (Val1 and Val2) from which I need to subtract a total (Calc) into two new columns (Net_Val1 and Net_Val2). I need to subtract my value in Calc proportionately between Val1 and Val2, however there are some conditions that need to be met. I'm calculating the value to subtract into Val1_C and Val2_C.

1. If Val2 is 0 (or less than 0) the full amount is subtracted from Val1 (see rows 2-4)
2. I can only reduce Val2 by a half maximum. Anything remaining is subtracted from Val1 (see rows 5, 7, 8)
3. Because of #2 above, Val2 can never be reduced to negative. Val1 can be negative.
4. If both Val1 and Val2 are positive, and none of the above apply, then proportion the value in Calc between Val1 and Val2, eg

   =[@Calc]/SUM([@[Val1]:[Val2]])*[@Val1]

   (see rows 6, 9)

So I can get #1 and #4 into an IFS() formula OK (I think), but I'm having a hard time incorporating #2...

=IFS([@Val2]<=0,[@Calc],TRUE,[@Calc]/SUM([@[Val1]:[Val2]])*[@Val1])

although this also falls over a bit if Val1 is a negative.

I'd appreciate a point in the right direction please. Here is my sample data, with what I expect to see in Val1_C and Val2_C. I've struggled to put this all into words, so hopefully it makes sense enough.

MyCalcTesting.xlsx
	A	B	C	D	E	F	G
1	Val1	Val2	Val1_C	Val2_C	Calc	Net_Val1	Net_Val2
2	475	0	1000		1000	-525	0
3	1450	0	1000		1000	450	0
4	-2450	0	1000		1000	-3450	0
5	-1500	600	700	300	1000	-2200	300
6	3950	210	949.52	50.48	1000	3000.48	159.52
7	-100	100	900	50	1000	-1000	50
8	225	1120	440	560	1000	-215	560
9	375	4050	84.75	915.25	1000	290.25	3134.75
Sheet2

Cell Formulas
Range	Formula
E2:E9	E2	=1000
F2:F9	F2	=[@Val1]-[@[Val1_C]]
G2:G9	G2	=[@Val2]-[@[Val2_C]]