The Mod Bob models best on 30M, and it matches the gain I get on my DX Engineering DV-40-P phased vertical array.
The pattern is very close to a Bobtail Curtain on 30M, but I think its more like an Extended Double Zepp if you just look at the horizontal part, and almost three elements phased almost like a Bobtail if you look at the verticals only.
What makes this so much fun is that the antenna is a “hybrid” just like the 30M band itself. From the ARRL Antenna Book:
10.1-10.15 MHz (30 m)
The 30-m band is unique because it shares characteristics of both daytime and nighttime bands. D-layer absorption is not a significant factor. Communication up to 3000 km (1900 mi) is typical during the daytime, and this extends halfway around the world via all-darkness paths. The band is generally open via F2 on a 24-hour basis, but during a solar minimum, the MUF on some DX paths may drop below 10 MHz at night. Under these conditions, 30 m adopts the characteristics of the daytime bands at 14 MHz and higher. The 30-m band shows the least variation in conditions over the 11-year solar cycle, thus making it generally useful for long-distance communication anytime.
I do remember how 30M can behave a lot like 40M at night and early morning, but I can’t say that I have ever seen it behave much like 20M. However, I haven’t really monitored it as much as I have 40 and 20M, so, with this antenna, maybe I will start checking into 30M more.