Firstly, we intend to migrate fixed widgets like this to being Code Studio based (hopefully 2021). That way, if you want to tweak it (as you do) or extend its functionality your own team can take a copy of it and change it yourself.
The way this is designed at the moment is, based upon your selection of the decision, it chooses which sub page to display. (Defaulting to the one associated with the overall gateway, and displaying a more specific one when a decision is selected). It would be slightly fiddly to change this.
Therefore, we are a little reluctant to make changes like this, instead wanted to invest in the longer-term goal (above).
A possible alternative is to split your single step in two - the first holds the sub page and takes input and the second has the decision associated with it. (That decision could be automatically completed if it can be derived from inputs on the previous step).
If that doesn’t satisfy we could look at this again.