I topped the two main side branches on day 22 and am letting them grow out 4 each (2 per side) to give 8 tops in total. This is not a proper mainline but there you go, it should give me what I want.
Due to the squat, bushy nature of these girls, it is hard to see the pins that I am training them with but it will get much clearer as they develop and I start pruning unwanted growth. At his stage I am using wire to keep everything flat, spreading the tops out in the horizontal plane.
You can see some nutrient burn - this was my mistake - I suddenly dropped the humidity (from about 70% to 50%) and they took up too much nutrient. As soon as I restored the humidity levels, they were fine.
From day 28 I am removing all the unwanted side growth and now you can see how the wire is holding the structure I want.
The Blue Gelato is bottom right in the day 28 pics and you can see I damaged 2 branches so it will end up having only 6 tops.
@Godesskat, Thank you mate - at the risk of jinxing the grow, I'm fairly confident this will be my best ever. These plants are just so full of life, it's quite a joy to see.