Aspires Export to STL function has no preference for units, it just exports as whatever units the user has chosen to create the job in. This appears to be the same behaviour as Fusion. When you mentioned exporting to your slicer program from an inch model in Fusion, are you just saving the STL file out, or sending it to your slicer program directly. There is a bug in Fusion where it would convert inch models incorrectly to mm when it was sending to an open slicer program, see the last post here:https://forums.autodesk.com/t5/fusion-3 ... -p/6414039
However this, as shown in that thread, is a bug and not the expected behaviour. The expected behaviour in Fusion is to use the document units when exporting to STL which is the same process Aspire uses.
Maybe the above bug might be why you have been seeing differences?