After fiddling around for a long time I was able to get bursts on either pole and even "Antonio" style ones that went straight up the middle between the poles. These could not be locked reliably with the PLL however, and the adjustments for soft switching were very sensitive (iow- I only ever got it to work once)
On the other hand, bursts using the upper pole were stable and easy to lock. The PLL made a good job of compensating when the secondary was loaded, even to the point of total open or short circuit.
Bursts using the lower pole were only possible if some hard switching of leading current could be allowed over the first few cycles. Any attempt to tune this leading current out just made the system lock to the upper pole instead.