Will Group tags affect a simplified field notation?

Hi All,

I have 2 fields which I would like to subtract.

The first field is named Group99911.px1offer1 and the second is named Group9991.px1over1

In a previous form before I used the group tag to simplfy the coding, the calculation in the simplified field notation worked fine as px1offer1-px1over1

Since using the Group tags the simplified filed notation does not work as Group99911.px1offer1-Group9991.px1over1

I have also checked the field calculation order is correct, however both fields are manual entry but are in the correct order

Have I over looked something glaringly obvious or will Group tag not work in the simplified notation ?

TIA