Yeah it'll definitely find a way, mine was rammed in a corner with a bogwood blocking it into a space about 4inches square, it multiplied on top of each other or anywhere it could find a space. Due to the fairly small root structure and thin leaves as long as there are enough nutrients, co2 and light it'll grow. Runners will grow even if they are completely shaded like almost all of mine were, they seem to take nutrients from the mother plants rather than trying to create their own until they reach high enough to use the light.
It will grow very densely with runners if it doesn't have room to grow outwards. The piece in the 4 inches square of gravel turned into over 30 runners in 6 weeks. Buy some if you can't wait, but you might kick yourself when you get to the point I was at where you are throwing out 2-3 runners a week. Vallis would have quite happily taken over the entire tank. When I removed them there was the original plant with really thick wide leaves and another 25-30 plants all attached by runner stems that came out all attached together.
I'm ordering probably another five vallis plants so I'm hoping I can work something out to fix it, hey if it stacks up deep enough it won't be able to make a gap that big lol!
