signal analysis and synthesis with different window length and FFT length
MATLAB documentation says for element-wise operators + and .*:


  Numeric or string inputs A and B must either be the same size or have
  sizes that are compatible (for example, A is an M-by-N matrix and B is
  a scalar or 1-by-N row vector).


Further explanation:


  Two inputs have compatible sizes if, for every dimension, the dimension sizes of the inputs are either the same or one of them is 1.


It looks to me like your code violates this if winLen &lt; FFTLen.