Tom,

The clever thing with the Arrow implementation is its dual band version
where it is mechanically elegant. Does it lend itself to scaling up by near
three times?

It isn't clear that you wanted a dual band version, though there are hints.

If you are looking for a single band antenna as implied in the subject...

As you have noted, the total height of the J pole for 6m is a potential
issue.

You could look at it as essentially an end fed half wave with a rather
large impedance matching device (~1.5m).

There are other more compact ways to impedance match an end fed half wave.
The question for you is whether you can devise a robust implementation.

Is there advantage in using aluminium tube over wire? Well, obviously the
wire needs support, but perhaps a telescoping fibreglass pole and wire with
a matching network in a PVC box is another robust option.

Keep in mind that end feeding a half wave reduces the common mode current
flowing to the feedline, the feed point voltage is highest at exactly a
half wave. You might find a slightly shorter radiator to deliver most of
the 'ground independent' feed, but with slightly less demands on the
voltage rating of the matching network. It may be prudent to make your
matching network adjustable to provide for locations where proximity to
other things changes the tuning.

I said fibreglass (meaning literally glass reinforced plastic), and that
doesn't include graphite or carbon fibre. A lot of these fishing poles are
now made from graphite, and that introduces potential for loss.

BTW, I am not sure that your 'design' of the pattern is all that sound,
however real antennas near lossy soil just don't have very low angle major
lobes... so what you want happens for probably any low makeshift antenna.

Owen