I have some questions in regard of the problems you are having. I would like to try and help you.
Let's see if I understand it correctly:
Since you started planning backwards, you are experiencing the problem that the quantity of the expected materials in the production order differs from the original BOM?
Is it just concerning 1 item? Or are all materials changed?
When all materials have been changed, can you tell if it has changed by the same percentage?
As soon as the materials have been changed in the production order (tisfc0101), it will be changed in the material issue (ticst0101).
I am using Infor ERP LN and I am planning backwards, but I can't see the planning method changing your material requirements.
What I can think of is that you might have a percentage of waist setup in you BOM. You can check it in session tibom1110m000. There are three colums
that might give you an explanation.
I don't know what the column names are in English, cause mine are in Dutch.
I hope this helps you somewhat.