tbh it did sound a bit weird to me too but thats what that guy from the garden centre said i should do with it. this viv doesnt have light fittings and the centre had non in stock until this wednesday so the earliest time i can get there will be next sunday. atm its the only heat source. the temp gauge says its fine but if you guys think its a problem. how would u say i resolve it with no light fitting?
I would put it on the floor of the viv, covered with something (even it its just newspaper) for the time being. If you were to stick with a heatmat for a bit then you would need it approx 1/3 of the floor space and covered with something like lino. However, the best sourceof heat for a large bodied snake like a Royal is either Ceramic or Red Bulb.
the thing with mats is that they heat wot ever is in contact with them. cos yours is on the side of the viv with nothing touching it i would say it is doing very little with reguards to the temp.
as was mentioned before i would either locate it on the floor or use a lamp/ceramic to heat the viv....