Changing Arithmetic to fixed point for a multistage FIR design

I am trying to observe the fixed point effects of a multistage decimation. However, the system object does not seem to change arithmetic to fixed point. For example:

fdDecim = fdesign.decimator(M,'lowpass', Fpass, Fstop, Apass, Astop);
msDecim = design( fdDecim, 'multistage', 'Usehalfbands', true, 'SystemObject', true);
msDecim.Stage1.CoefficientsDataType = 'Custom';
msDecim.Stage1.ProductDataType = 'Custom';
msDecim.Stage1.AccumulatorDataType = 'Custom';
msDecim.Stage2.CoefficientsDataType = 'Custom';
msDecim.Stage2.ProductDataType = 'Custom';
msDecim.Stage2.AccumulatorDataType = 'Custom';
msDecim.Stage1.CustomCoefficientsDataType = numerictype([],32,31);
msDecim.Stage1.CustomAccumulatorDataType = numerictype([],32, 31);
msDecim.Stage1.CustomProductDataType = numerictype([],32, 31);
msDecim.Stage2.CustomCoefficientsDataType = numerictype([],32,31);
msDecim.Stage2.CustomAccumulatorDataType = numerictype([],32, 31);
msDecim.Stage2.CustomProductDataType = numerictype([],32, 31);

But info(msDecim) shows Arithmetic : double

What else do I need to set to convert this object to a fixed point implementation?