Flip now and then LST, not the other way around in your situation. Normally it's LST in veg, but here's the "surprise" about that -- let's say you LST 8" off the vertical height, which now is 12". That doesn't mean you have a 12" plant that will double in size during flower to 24".
You still have a 20" plant that will double to 40" minus the 8" saved by LST. So you plant will end up at 32".
I just learned this the hard way -- LST like crazy, flipped at what I thought was 18", when it was really more like 25" -- the my plants are sativa dom and have almost tripled in height. I had to get a bigger tent, rush from Amazon.