I've recognized that my design uses way too much DSP-Slices than it should, so I looked at the generated model in detail and also the corresponding vhdl-files. To my surprise I found that the wordlength of the multipliers was twice (from 32 to 64) as originally specified. This happens regardless of whether the wordlength/datatype is inherited or specified. Why does this happen and is there a way to suppress this behavior?
The input fixed-point data types have the same wordlength and do not change in the generated model or code.