Hello Steve and Jay,

Results were :

The loop is actually fairly omnidirectional - just not at 0 degrees
elevation. As you move up from 0 degrees elevation the pattern starts to
"fill in" nicely in the direction of the "nulls".

The nulls are minimal at an elevation of about 30 degrees (but still -15..20dB)

Not sure, but I think you can prove this with a small receive loop while
nulling out a local broadcast station. Tilt the loop even slightly off
vertical and away goes your null in a hurry.