This is a great question.
By default, the Mask is forcedly centered, and redefinition does not occur, but you can move it right away when displayed.
Example
Ext.net.Mask.show({ msg : 'testing' }); Ext.fly(Ext.dom.Query.selectNode(".x-mask-msg")).setStyle({ top: "30px", left: "30px"});
Hope this helps.
source share