Re: 160 meter delta loop.
- It will have effect, but on 160 I would not worry about it.
I would keep the feed point away fron the buildings, just for good measure.
However, keep in mind that on 160 the loop feedpoint impedance is around 25 Ohms at 10 meters high, and goes up with an additional height.
My experience with "nulls" at higher frequencies - the antenna automatically (!) "picks" the best propagation path for you!
I newer used it on 160, and it may be just a great cloud burner due to the height.
73 AA7EJ Vaclav