Revert to older firmware. The default height was adjusted for newer machines, so the old, unsupported machines no longer work well. You can do a search on here for others with the same issue. For the mini1, I think it was the last marlin 1.x firmware that worked well.
Or, you could modify the firmware and get it working on a more up-to-date marlin if you want to do a little math to fix the Z height issue.