[MAYA] Transfer Maps - Transfer Normal Map

I am trying to transfer a tangent space normal map on an object to a new tangent space normal map for a lower-poly version of the same model.

however, the normal map that is output doesn’t appear to be a correct tangent space map, it looks like the input tangent space map was interpreted as a bump map, then output as a tangent space map.

i’m using maya 2015, sp5. Anyone got any advice on using the Transfer Map tools to transfer normal maps?