Hi Graham,
jib and mizzen only
I have used this combination a lot in other boats, particularly the Salcombe yawl and the Devon yawls.
Both in the 80s, at the time, they were older boats with poor sails.
They acted pretty much as you describe. You need more wind, for more power, to create headway sufficient to steer the boat and persuaded it to go upwind. we did not have instruments in those days so I cannot tell you precise numbers. I do remember we had to gybe them, when tacking failed. importantly we did get them upwind if it was blowing..
We used this combo when it was too windy to teach in wayfarers and the 14ft clinker one designs we had.