Trapezoid Room Room Acoustics

Would appreciate help on placement in a trapezoid room (or irregular quadrilateral) ie no 2 parallel sides. It also has a double height ceiling with a full panel of glass on one side. The remaining walls are concrete with marble floor. Should I place speakers along a long wall or put them on the narrow end or the wide end?

Despite all the hard surfaces, the slap echo is not too excessive maybe due to the lack of parallel walls.

Thanks