Looking good, Red, will be watching as they set buds. In case you haven't peeked at my light intensity thread, I have pretty well decided that light strength is having negligible effect on KEEPING my plants from stretching. I already know that good light strength improves bud density / quality, but my thought of it keeping the plants from stretching was misplaced. IThree days ago I swapped out the light over my TH Seeds Auto Original BubbleGum. She was 9 days in from transplant and only 3" tall. Healthy as she could be but short. But I took out the Mars and hung my trusty 250W HID cooltube reflector, and in three days she has gone from 3" to 6.5". Plus she is opening up beautifully and all the lower / side branches are already stretching to catch up. I intend to leave the HID in place, switch from metal halide to high pressure sodium when she shows, and leave that in place until she stretches enough to complete LST. Once that's done I'm going to re-hang the Mars -700 LED to harden the buds & finish the grow.
Final verdict - I believe it's the light spectrum rather than strength that was encouraging every one of my LED grows to not stretch. More research to be done - you saw some decent stretch under your Mars 300; all I can speculate is yours was closer to a full spectrum than my 700 or the Pro Cree-128. We'll see.
I believe BigSm0's COB's use full spectrum? Do you have the Kelvin ratings on yours? Still going to chase this to confirm why my plants stretch under HID and not LED; and if there is a spectrum within LED technology that comes close to matching my old HID performance.
Anyway, your girls are looking awesome. Keep the progress reports coming! Later.