I am sorry to say that custom dimensions for the tiles are not supported at the moment and we cannot fix issues arising from them. What I can suggest is overriding the CSS classes for the width of the elements that hold the tiles (rtlistWrapper for starters, as this is the element that creates the columns; rtlistGroup may also need some tweaking). You can access them with jQuery in the OnClientLoad event
of the control if you need to modify them dynamically (sender.get_element() gets the main div of the control).
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