screen variant customization for sales docs via SHD0

Hello Colleagues,

Need your help with the following problem

I want to make fields vbak-guebg and vbak-gueen visible on tab Sales in sales document with sales document category "C"

I decided to achieve it with creation transaction and screen variant in shd0 by customizing them as visible.

but when I go to the the tab Sales I don't see those fields.

I use the following parameters

program name SAPMV45A

screen number - 4440

I even made all fields visible on that screen via tx shd0 to make sure I do customizing correctly and made sure that changes work for other fields but not for those ones I need.

for document with sales document category "G" everything is OK (fields appear)

may be some restriction hardcoded in SAP (in PBO or somewhere else) I tried to check PBO but didn't find something there.

would you please help to understand why fields VBAK-GUEBG and VBAK -GUEEN don't become visible on screen 4440

even if I customized them as visible in transaction and screen variant

Thank you