Hi Tegwyn,
Unfortunately there's no good way to use the same field on the same project, whether its on a separate custom form or not.
As you know if you have the same field on the same form, you have to name it a bit different such as Leading KPI 1, Leading KPI 2, etc. But can get messy when it comes time to create a report.
But even if you create separate custom forms and place them all on the same project, any field with the exact same name will over right all other fields with that same name. So if you have Leading KPI on your Form 1, whatever you select for that KPI field will auto-fill that same selection on that same field in the rest of your forms attached to that project.
We have some forms where we've built that Field 1, Field 2, etc. And it does get real messy for reporting. We're considering creating separate issues on the project for each item those fields relate to. But haven't quite gotten there yet. That's one of our 2020 goals, cleaning up our custom forms and making those kinds of changes where we can.