I am afraid responsive layout of the RadTileList control is not available yet and changing the number of rows on the client is not possible. We do have plans to improve this, but at this point I cannot confirm an ETA. Once available, the feature will be listed in the release notes.
On groups - the number of rows is valid for all groups in the control and cannot be changed per group. As for custom tile sizes - at this point I cannot confirm their proper functioning in a RadTileList because this is related to changing the dimensions of the control (i.e. all its calculations) and is also related to a responsive layout.
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