When you use a PSD with SQP model, the PSD diameter is the bounding diameter. The data check uses the max of all defined diameters (whether they are actually used or not) when comparing particle size and cell size. We should improve that in the next release, so it only the max diameter of used particles is considered. However, I would suggest to always define the baseline particle size such that its diameter does not exceed the max diameter of the PSD. That way you can switch back and forth between the baseline and PSD particles or use both the baseline and PSD in several ICs or BCs.