I often wonder where NVIS gets this mystical notion. This isn't rocket science. You said earlier... All it takes is just one example to disprove this absolute statement and many folks have many examples from direct experience and hard data. We know a ground mounted vertical over a nice conductive screen will have the least NVIS performance... but not quite none. Yeah sure an antenna designed specifically to launch straight up (horizontal dipole or STL) is going to be much better that a mobile vertical, but that null over the mobile vertical isn't as deep or narrow as idealized circumstances might suggest thanks to all the other currents running around the vehicle body. I'm kind of surprised at you Alan. It's your inspirations that have helped folks squeeze every little bit of efficiency from an HF mobile install... especially for the lower bands. People apply them and, behold, they are doing short hop skywave on applicable NVIS wavelengths. From what we see, the radio circuit behavior is such the antenna system inefficiencies aren't enough to prevent rather booming signals. Some folks arrange small transmitting loops on their vehicles for state QSO parties to maximize the skywave. They work quite well, but we find time and again, those with the larger, beefier, Scorpion-like screwdrivers (installed with your thoughts and ideas Alan) simply have no problem working the entire state on, of late, 80m for almost the entire event. The circuit viability fluctuates perfectly in sync with the ebb and flow all the fixed stations experience on their low horizontal dipoles or 1 wavelength horizontal loops. Put simply, if you are a fixed station working the VAQP and want to reach the HF mobiles with 40 and 80m, a skywave specific antenna is a must because that's where the mobiles, inefficient though they are, can be worked... in the case of W4GO in my article, with astounding margin. In summary, there are technically better ways to work NVIS on your mobile than a good ole' screwdriver, but if you pay attention to Alan's installation notes, a screwdriver will provide "good enough" service for this flavor of propagation providing a good return on the investment in money and hassle.