There's no single answer because, as Cecil said, the response changes
markedly with frequency.

Maximum radiation will be broadside at frequencies where it is a half-
wave, and it will progressively develop multiple lobes and nulls as
the frequency is increased.

The common-mode current on the "vertical radiator" tends to fill in
some of those nulls, but its contribution is also very frequency-
dependent.

Here's an example of the difference that the "vertical radiator" makes
to a 132ft OCF dipole on 20m - one of the bands where it has most
effect. Red trace is the azimuth response at 10 degrees elevation
without the vertical radiator; the blue trace is with it:

http://www.karinya.net/g3txq/temp/ocf_low_angle.png

73,
Steve G3TXQ