It may take a while to see a change, we could do with some imput from a plant guru. I'm only still learning, but it is something to do with gas exchange across the leaves.
I found a quote from ceg4048 over on UKAPS
"There are lots of environmental conditions under which the plant needs to change it's growth rate. This normally happens under environmental stress. When the plant is under these stress the concentration of ethylene rises and various mechanisms respond to the concentration rise. One of the most extreme environmental stresses a plant can face is that of being flooded. Flooding the plant traps gasses, prevents their movement and causes buildup. In general, gasses are about 10,000X less soluble in water than in air. That's why CO2 uptake is such an acute a problem for aquatic plants. When the plant is flooded ethylene is trapped and it's concentration build. The reaction of the plant is to immediately grow upwards to reach the surface where there is air and where access to atmospheric gasses are in greater abundance. In effect, the plant is building a snorkel by having straggly growth.
There are a couple of ways that we fight the straggly growth. One way is to simply cut the growth. The new leaves that grow are submerged leaves and they are better adapted to a flooded environment, so they tend to grow less straggly. The penalty though is that cut leaves do not produce food, so recovery is slow. Another way is to have better flow. More flow across the leaf means better diffusion of gasses so ethylene can be removed more quickly and CO2 and O2 also have better movement.
Carpet plants such as HC, grasses, P. helferi, Glosso and so forth are real victims of this optical illusion. "I need more light" is a famous battle cry when most see upwards growth. This is exactly the wrong thing to do. Better that you have more flow, more CO2 which then produces more O2. This improves the gas exchange, lowers the ethylene concentration buildup and relaxes the plant to grow more horizontal instead of desperately grasping for air.
People are so hypnotized by light it's incredible. Every problem that occurs must be because they need more light..."