Hi @gmonbel,
In the current version, this plugin only supports calculations that are defined in the same group. We mentioned this in the plugin description. So the short answer is that this simply not not supported.
The technical reason for this restriction is that fields that are defined in a different group are not guaranteed to show up ob the same screen when editing (they can have different display rules in ACF). This has an effect on both real time updates via Ajax and during the save process. We would have to change the method we access fields.
But we’re eager to improve our plugin. This is something that we’re more than happy to look in to. To do so, it would be a great help to get some more details about your setup and what you want to achieve.
We regard this as a feature request, so we’re marking this issue as closed (you can still reply to provide details).
