A scone exists for one purpose, and one purpose alone. And that is to facilitate the consumption of as much clotted cream as possible.
So, in this scheme of things, the jam’s role is much like that of butter in a sandwich: it’s not there to feature in its own right, it’s there to help you eat more of the other, better stuff without your mouth getting stuck together or any other unpleasantness occurring. (Jam has precisely the same role in a PBJ sandwich, where a thin layer of it lets you eat twice as much peanut butter without gluing your face shut for the rest of the day.)
A thin layer of jam is plenty: just like butter on bread. And then on top of this you spoon as much clotted cream as you have available. If the scone isn’t twice its height by the time you’ve stuck cream on it then something’s gone wrong. (If your tea shop has not provided enough cream for this, go and shout rudely at them.)
Loaded up properly like this, one scone should be quite adequate, leaving you at the point of feeling borderline sick but massively satisfied with the amount of clotted cream you’ve put away, and ready for the rest of the day down the middle class tin mine.