Mike,
Sorry for a misunderstanding.
If all that concerns you is matching  then it does not matter if there is a
ferrite core or no ferrite core, but if you are also interested in getting
greater efficiency by obtaining more radiation from the top end, then my
comments are valid.  The simple point that I was making is well illustrated
by considering an ordinary ferrite core aerial on a receiver, the
efficiency on reception incrreases but the efficiency on transmission
decreases by the same factor - the ratio of B to H.   So if you are not
interested in getting a bit more radiation from the top end but only want
to change the matching impedance, please ignore my comment and go ahead!
With kind regards,
Roger.