Conical interface shapes like in YAG-growth are simulated using NaNO3 melt growth systems. We have studied in detail the effect of the magnitude of the heat flux through the crystal on the interface deflection at crystal rotation rates near zero. The convection in the melt, driven by buoyancy and thermocapillary, was changed by varying either the radial temperature gradient in the melt, or by changing the melt level or by the application of cooling shields above the free melt surface. All these parameters have a significant influence on the crystal rotation rate which has to be applied to grow the crystal with flat interface. Comparison with numerical simulation is made using the experimental values as input parameters. (C) 2004 Elsevier B.V. All rights reserved.