to lengthen is the better idea, and you have more place/distance with the POTY reflector disk to the feed arm.
You have also a wider area to slide the POTY in direction to the dish reflector to find the best position for focus.
Here is what I came up with last night. With this setup, I could hear the beacon and some QSOs, but signals were weak. On TX, I could not see my signal on the waterfall. So more work needed.
My guess is that the problem is the position of the feed. The feed is now the same distance from the feed as it was in the original, where it was working well, but in the original the bottom of the reflector was touching the mount, now it is about 2 cm above, so it is not pointing to the same spot on the dish. Any way to fix this?