OK, you may want to revise the first cell height. DPM won't check wall collision unless it's in the near wall cell, at one micron diameter at the point the parcel enters the cell it should have hit the wall.
It's a common discussion here when introducing aero engineers to multiphase. They're very familiar with y+ from their academic CFD courses but not so much with how the more complex models behave. It's also why I have very little to do with modelling cars and aeroplanes....
You are navigating away from the AIS Discovery experience