IP Plan yearly value and post via invers formula to monthly value

Hello experts

I use a input ready formula to enter and plan the  year value.

So I try  to post the yearly values down on monthly level using  the invers formula technique .

Lets say operand JAN would then take the yearly value divided by 12 and the input ready formula is then the sum of all 12 operands ( Jan to Dec)

I though it is a smart way to do it instead to use planning function ( Standard, or Fox, or Exit).

However the input ready formula just updates January and adjust the formula. The Feb, Marz etc gets untouched.

Meanwhile I have doubts, that the invers formula technique may help me in that case.

Have someone a good idea how to solve it?

Thanks a lot for your inputs

Christian

PS: I use BW 7.3