Tying them down, hard training them will not affect potency...get a screen of chicken wire and a frame, and as the plant starts to flower start tying in the buds withthem little tie wraps....pinch out any internodes and buds below the screen, channeling all the energy into the buds growing from the screen. easier trimming too.
Rootboundedness will affect the yield far more. Use the biggest pots you can find, this period just before flowering is when the rootmasss explodes and gives the plant the ability to take in enough nutrients and water to produce bud. Root development slows down and eventually stops during flowering, but before they flower pot them up every time the roots are filling your container/growing medium.
If the leaves are fat they are likely indicas (7-10weeks flowering) rather than sativas, which is good as sativas (13-20weeks flowering)will never finish flowering inthis country before the frosts come, maybe in polytunnels it could be done

It's probably a hybrid indica sativa as most commonly sold seeds are now, and is probably 8-9 weeks flowring time....
5-10mm internodal spacing sounds a bit too short to me, could be a symptom of them being rootbound...a stocky plant is nice, easy to handle, but overly stocky restricts space for bud to grow, and increases your chances of mildew.
If the leaves are "deformed" you may be overfeeding them, are they curling in at the tips and edges?
you really have to pot up.....growth explodes during the first week or two of flowering anyway, with plants easily stretching to twice their height/size for indicas, and sativas even more. And don't feed them for at least a week after you've pottted up, wait till you can see roots throughthe holes in thepot.