The won't really stretch, they'll just develop poorly on the bottom after a certain height. I've grown years old, very thick mothers under them. The biggest issue is they'll outgrow the horizontal space quickly unless you have a lot of room / lights.
I'm not really seeing your point. The one on the left looks like it hasn't stretched aside from where you raised the light too high. The ratty sativa on the right looks ratty and unloved.
Mine didn't ever have any issues and they would touch them sometimes. I tried keeping them 2" above the canopy though.
