Thank you WFab and DimKoutris for you replies.
Yeah, the 0 -1 workflow is a challenge. I'd personally prefer a .5 ground level so that things like zero borders worked as expected. Then you could equalise the edges to .5 and have a crater above and below. Currently there is no way to buld a crater and zero it's edges. Similarly, bomber expects the input to be at 0 height as well or it additively stacks the duplicates.
I have tried inverting before bombing and also making my own but have kind of given up on it which is a shame. I'm now exploring other avenues to at leat create a base line scatter before importing that as a file inot gaea and continuing.