How does mesh size of Barium Chloride affect sulfate results via turbidimetric method?

I am analyzing sulfate using Standard Methods 4500 $\ce{SO4 ^2-}$ E (turbidimetric method) using $\ce{BaCl2}$ and measuring %T at 420 nm. In the past, we used an appropriate 20-30 mesh size for the $\ce{BaCl2}$; however, it appears that it only is sold in mesh size 10 now. 


This smaller mesh size is causing higher %T in the standards (less turbidity), but a check standard will still give accurate results ($r^2$ = 0.98). The main issue is sample results being anywhere from 3-10 mg/L too high (e.g., routine samples of 7-8 mg/L now give 10-11 mg/L, and 5-6 mg/L now is 15 mg/L). How does the size of the crystals affect the sample results? Is there any way to correct the results or in some way account for the smaller mesh size?


