This is nothing more than the discredited "Column" method of T/A lowering.
Frankly, I find the method and results difficult to accept, and chem_geek and waterbear are two of our best on T/A chemistry.

Are you sure of your chemicals and how you ran your tests? When pH drops, TA does as well, but a .3 drop shouldn't be enough to resolve a TA difference of 190 down to 100.

Carl