Due to the intensive mixing in the rotary coater each particle will have the same chance to obtain the liquid and powder material and the enlargement of each individual particle highly depend on its surface area.

Thus, the size uniformity of the original seed lot highly affects the final product uniformity. 

 

Depending on the desired level of product uniformity it may be necessary to calibrate the original seed lot and except the loss of an non-coated fraction or coat the separate size fractions.

Another option would be to include additional screening & enlargement steps during the coating process which will demand additional coating equipment.

It will be clear that either way the coating process becomes more complicated and less efficient and process time will increase.