I agree, but it depends on your location and time of year
That's intensity and duration, not light travel angle.
The sun is a single point of light, being cast on a sphere. There will always be more light on the sides of the plant because the plants are at an angle the majority of daylight hours. If this were not true, shadows wouldn't be present NEXT TO the plant 80% of the day, but only 20% or less. Before any one argues, grab a flashlight and a ball. Shine the light on any spot from any angle. Now move a stick along the ball as if it were a plant. BINGO!
Now the inevitable question...Why do plants grow up, not out?
This happens because plants don't look for light, necessarily, but rather the first SOURCE of light each morning, and the last of it in the evening. As the sun hits the horizon, the light beam of the sun slowly drops from above. Because of geological formations, houses, Etc. there may be a corner, or wall, that receives light first, but the rest of the garden is shadowed by a tree. The plant will head for the wall because it wants the most amount of time in the light as possible. This is why "Street light pruning" is so funny. Random branches growing in circles, loops, spirals, chasing what it thinks is the sunrise, and sunset! So they are growing away from shadows, which is usually up. For this reason, "2 and 10 O'clock" are the best locations for primary light. This is awkward indoors, because we use rectangular construction techniques. Right?