K4SAV Hello can you expound on why a 23 ft vertical is performing as you stated "too high an angle for 10m,12m."and What modeling software did you use?
23ft on 10m should be a pretty good length to provide a good utility for low angle pattern there.
Any working modeling program will show this.
5/8 wave on 10m is about 20' (hence all the CB antennas of this dimension.) Anything long than
that will result in less radiation at low angles on 10m. It doesn't drop off that sharply, however,
as long as you look at the actual radiation at a specific angle
rather than simply the angle
where radiation is maximum (because there are multiple lobes in the pattern.)
Because the radiation from the bottom of the vertical is often broken up by nearby buildings, etc.,
using 3/4 wavelength isn't that much worse than 5/8, and even the standard 43' vertical is only
1dB or 2 dB down on 10m and 15m from the optimum 5/8 wavelength levels. So longer antennas
tend to still be usable. Shortening it too much reduces efficiency on the lower bands, however,
and I wouldn't want to go any shorter than perhaps 24' if effectiveness on 40m is important (unless
you provide some sort of loading in the center or top of the antenna.)
So increasing the height of the vertical will improve 40m performance somewhat, while shortening it
may improve 10 slightly.