The limit is (I think) the sum of the granular phases. But, if you have two sizes then the smaller can fit into the gaps so you might want to increase the value, or start using a UDF to adjust things the limit based on volume fractions.
https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v231/en/flu_ug/flu_ug_sec_mphase_using_steps_eulerian.html%23flu_ug_sec_eulermp_using_phases
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