Do you mean the 'Microscale' product? If so, then like any matt varnish, particularly if enamel type, it needs a lot of stirring in order for the matting agent to mix into the carrier fully. Even then, very often a semi-matt finish is the result.
I 'binned' all forms of matt clear some years ago, for this very reason, and also because, after time, yellowing will occur. I now use Tamiya Flat Base, mixed with Johnson's Klear (Future), to provide anything from a slightly subdued gloss, to full matt.
It doesn't need much of the FB to achieve a full matt, but too much will cause a 'chalky' appearance, so some experimentation is needed to achieve what's required, then test on a piece of painted scrap.