Other than locating an antenna as high as posible and in open space, are there

"sweet spots" that behave like funnels for radio waves?
....
Ron, W1WBV

There are.
I would group them into two huge groups: one, large geography, two, immediate
surroundings.

Geography and ground conditions can focus or disperse radio waves as well as
contribute to the formation of the antenna pattern. Example would be antennas
on sloping hills, bluff on the shore of ocean.

Immediate surroundings can cause reflections and sweet spots. Example I came
across was small loop next to the Beverage. It had better performance than
either lone antenna, better S/N. Another contributor are the guy wires,
surrounding towers and anything metallic. Easily seen with mobile setup.

Yuri, K3BU.us