Sounds fun.

Did you try adjusting the length of the driven element, if it is
adjustable? Just a wee bit, near that 3:1 SWR point?

Also, seems you might be better served with a 1:1 coil of coax as a
choke, unless I misunderstand. You should be able to get a direct match
to the coax.

Don't know for sure, but it seems like the driven element needs to be a
wee bit short for gamma type matches. Hmmm, I feel an Uda attack coming on.

(Hey lets give the grad student some credit! He probably did all the
real work, while Yagi was back in the lab, reading Uda's notes and
tossing back saki. That's how it works here in the US, aina, 'cept they
drink Chivas...)

good luck!

73, w4kaz