Generally, if you are doing anything more than loading in a straight height/bump bitmap into the Bump slot, then you should use a CoronaBumpConverter, or most likely experience incorrect results.
If using a normal and a bump/height bitmap together, then use your normal map as you would normally do (pun intended) by plugging it into the 'Normal' slot, then same as above, you are doing anything more than loading in a straight height/bump map into the 'Additional Bump' slot, then you should use a CoronaBumpConverter, or most likely experience incorrect results.