I think you mean that your DBX had a pre-engineered 5A FSDv1?I engineered my shuttlebus Diamondback Explorer, which with a regular FSD had a range of 73.96ly using Increased Range and Mass Manager...
...but now it's got a range of just 74.18ly. That's an increase of just 0.22ly.
The difference between that and the fully engineered 5A SCO is about that with that ship.
The nice thing is that you get the SCO capability without having to compromise on jump range.