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OK, think I can explain this.
In your initial example the top and left CSS properties are set correctly but the img element still has position set to static, so they won't do anything. You'd need to set it to absolute or relative positioning. The easiest way to that is through the cls config option.
As for your second example, with the panel, the problem is your choice of layout. Box layout isn't intended to be used directly like that. If you just get rid of the layout, or pick a suitable layout, it'll work fine.