Phototropism with clear vs translucent light

[Leucadian]

I have a recently acquired C. intermedia in a hanging pot, with roots that look like Gandalf's beard and pseudobulbs that point in every direction. The newest pseudobulbs, however, are growing almost vertical. I am growing this plant in a shade structure with 50% knitted shade cloth, and I suspect that it came from a greenhouse with an translucent covering. I'm curious as to why the new growth is vertical.

My theory is that with non-directional, diffuse light, the new growth can grow in any direction with no reduction in light energy. On the other hand, with an open shade cloth, the light is very directional and growth will tend toward the light. Why vertical and not 33 degrees from vertical (San Diego is at 33N) is another question.

This is more than academic to me since I am deciding on the covering for a planned greenhouse, and I could use a diffuse or clear polycarbonate sheeting, with or without additional shade cloth. Any ideas?