Water UFH Cracks bridging screed and blockwork - Tile Advice

[Sprotty]

We are currently at the planning stage for a floor with bifold windows and wet underfloor heating.

Basically the tiles near the windows will need to go over the screed and onto a concrete block on the perimeter (red arrows). I'm concerned that the screed with the insulation under it is likely to move (a little) and the concrete perimeter block will not - so we will end up with a crack line in any tiles we put over it (orange dotted line).

Is this actually a problem, and if so what do I do about it.

Thanks Simon