Shade house phal placement tips?

[Benno]

So I've got a shadehouse! Its 6 feet wide, 2 feet deep and 6 feet high (about all I had room for), and more than big enough ... for now. The front long side faces north (equivalent of south for the northern hermisphere folk). There is commercial grade 70% cloth on top, and 50% on all 4 sides. It has a just above ground level bottom shelf, a waist high middle shelf, and a half depth top shelf. At the peak of summer the sun is about 10 degrees off vertical (I'm in Australia, lattitude -27 degrees). The sun is quite powerful here...

I've got cattleyas, oncidiums, and dendrobians on the middle shelf where they will get the most light. The leaves get quite warm to the touch in the middle of the day, when the sun is coming through the 70% roof. But I can't figure out where to put phals.

I could add a layer of 50% shadecloth to the back part of the roof roof just on one section, and hang the phals up high (above the top shelf) off the back wall with pot clips - they'll only ever get the sun hitting them through the 70+50% cloth on the top, the sun won't be able to sneak in from the sides or the front so its quite simple, but counter intuitive.

If I put them on the bottom shelf where theoretically they belong, they'll still need another layer of 50% cloth above them under the middle shelf, plus on each side wall and the front wall, and they will not get filtered sunlight wherever there is a plant on the middle shelf. Surrounded by 2x50% layers of cloth which is only sometimes hit by direct sun and otherwise already in shade, they won't get much light when other plants are stopping sunlight from hitting the cloth. But if I don't have the extra layer, they will def get burnt in the periods where the sun can sneak through other plants....

Any suggestions on how I should go about this?