Geometries of SCl2(OCH3)2 and SF2(OCH3)2
Check the bond angles. The larger the angles around a bond, the more S character.
Electronegative elements prefer higher P character(Therefore less the bond angles).
Axial position has lesser bond angles.Hence higher electronegative element takes axial position.( F>O>Cl)

This concept however may not be applicable to every compound.