Mini-tablets with diameters of 2.0, 2.5, and 3.0 mm are coated in two different lab-scale fluidized bed coaters equipped with a Wurster draft tube. The main focus of the research is to evaluatethe inter-particle coating variability, and to assess the contribution of cycle time variation. Cycle times are measured using a photoluminescent tracer with a detector mounted on the top of thedraft tube. The number of passes variability is represented from 5 to 28% of the total coating variability. Additionally, transmittance measurements at the top of the Wurster draft tube are performedin order to assess the inter-particle sheltering effects. Transmittance results are correlated to the amount of coating deposited per single pass of the spray zone and are converted to solids volumefractions. The dynamics of the transmittance signal further reveal the persistence of a particle arrangement within the draft tube of the two different coaters. The gathered results give insight intothe different performance of two fluidized bed coaters in terms of inter-particle coating variability.