Dear Kim,
obj.UE_specific(uu).BLER contains the average BLER of each codeword separately (in case of MIMO with multiple data streams), whereas BLER_overall provides the average BLER over both codewords.
The third dimension of obj.UE_specific(uu).FER_coded represents the spatial dimension; that is, this is the sum over spatial streams (again in caso of MIMO with multiple data streams).
Best,
Stefan.