3.06 and 25fps/50fps modes

[Nick Payne]

I'm trying to download episodes 9 and 10 of Ken Burns' Vietnam War
series via the command line. The previous eight episodes (downloaded
with older versions of GiP) all downloaded as hlshd by specifying
--tvmode=best, but when I use --tvmode=best for episodes 9 and 10, they
are both downloading as dvfxhigh:

==============================================
D:\Users\Nick>get_iplayer --pid=b09bdyrl --tvmode=best

[]...

INFO: Downloading tv: 'The Vietnam War: Series 1 - 9. Fratricide (May
1970-March 1973) (b09bdyrl) [original]'
INFO: Downloaded: 49.65 MiB (00:54:39) @ 5.70 Mibit/s (dvfxhigh1) [audio]
INFO: Downloaded: 306.02 MiB (00:54:39) @ 9.83 Mibit/s (dvfxhigh1) [video]
==============================================

When I run get_iplayer --pid=b09bdyrl --info, it shows me that the modes
available are

modes:          original:
dvfhd1,dvfhd2,dvfsd1,dvfsd2,dvfhigh1,dvfhigh2,dvfxhigh1,dvfxhigh2,subtitles1

so no hls modes are available - it looks as though if I don't have
--fps50 specified, and no hls modes are available, then the recording
defaults to the *lowest* available quality. Is there a combination of
options I can specify to have highest available quality at 25fps as the
default and fall back to the highest available quality at 50fps if 25fps
is not available? According to the documentation, I can do it the other
way around if I specify --fps50 on the command line, as it will then
fall back to 25fps if no 50fps streams are available, but I find that
25fps is more than adequate for most content, and it downloads in half
the time.

Nick