My vhf dx operations are always on horizontal polarisation. Nearly always this is using tropospheric paths.
Es may produce different results as it involves the ionosphere. There has been a rash of articles and comments about what happens to polarisation in a plasma subjected to a magnetic field (ie. when a signal hits the ionosphere) and basically if I understand it correctly, the outcoming signal is circularly polarised, or at least has horizontal and vertically polarised components, whatever polarisation was used at the transmitter. This is also subject to conditions, hence the HF receiving antenna article in QST (with dual dipoles at 90 degree phase shifted combinations) that allowed you to receive signals as either Right hand circular or Left. With big differences in received signals and in QSB levels compared with a single polarisation antenna such as a dipole. Presumably these circular polarisation effects also apply to Es.
But my original comments were about using hand held radios and simple verticals on them. We have established a very reliable record of using horizontally polarised hand held radios (and hence, antennas) to get a massive improvement in signal level over non-line-of-sight paths. And this applies to both the compact helicals often provided as standard antennas and also the telescopic quarter waves that I now use as the normal antenna on my IC-V85.
This observation may well be contradicted by experiences people have when contacting repeaters that are typically vertically polarised and more significantly, cannot be changed to horizontal polarisation for such tests. It would be interesting to see how much better coverage was achieved by a circularly polarised antenna on repeaters. Given that typical commercial practice for the FM stereo system is to use a kind of elliptical polarisation, (ie H and V, not necessarily 90 degrees phase shifted) to make signals more readily receivable on various antennas people have stuffed behind their FM tuner, or on their ghetto blaster, or on their car, maybe this is something our repeater builders should consider. But none would be reading this...
Hence my thought that horizontal should be at least tested by people using HTs on 23cm FM. FM is not naturally associated with vertical polarisation and experiments are needed, folks. One instance is just an anecdote as Dr Karl says. Repeatable results, recorded in your log.
73 Andrew VK1DA/VK2UH