G'day Luke
Tis a hassle but that sounds a little too close even with a flameproof surface. Tiles over cement sheet will pick up quite a bit of heat being that close to the heater....granted there may not be much harm in that but I'd be questioning then how well the heater is going to perform its given task.
If there's not the airflow around it then it's not heating the air in the room as effectively as it might. Nor as efficiently as other choices for heating....