An attractive advantage of the capillary well microplate approach is the ability to conduct evaporative analyte preconcentration. We advance the use of hydrophobic materials for the wells which apart from reducing material loss through wetting also affords self entry into the well when the droplet size reduces below a critical value. Using Surface Evolver simulation without gravity, we find the critical diameters Dc fitting very well with theoretical results. When simulating the critical diameters D-c(G) with gravity included, the gravitational effect could only be ignored when the liquid volumes were small (difference of 5.7% with 5 mu L of liquid), but not when the liquid volumes were large (differences of more than 22% with 50 mu L of liquid). From this, we developed a modifying equation from a series of simulation results made to describe the gravitational effect. This modifying equation fitted the simulation results well in our simulation range (100 degrees <= theta <= 135 degrees and 1 mu L <= V <= 200 mu L). In simulating the condition of multiple wells underneath each droplet, we found that having more holes did not alter the critical diameters significantly. Consequently, the modifying relation should also generally express the critical diameter for multiple wells under a droplet. Crown Copyright (C) 2012 Published by Elsevier Inc. All rights reserved.