Cause of poor tomato blossom pollination?

This is the second year I've observed this: the indeterminate tomatoes in my greenhouse produce very  well on the lowest 3 feet, but little or nothing above that.  Currently the plants are 6-7 feet tall.

I had blossoms on the top 3-4 feet, but they didn't get pollinated.  Three things I've thought of:

1. About the time the higher blossoms are showing up, I put shade cloth on the greenhouse to keep the heat down.  The shade cloth was second-hand, so I don't know the amount of light transmission.  Is it possible the plants aren't receiving enough direct sunlight, even though they are warm enough?

2. The temps in the greenhouse haven't been above 90°.  Is that still too hot for them?

3. I have a circulation fan blowing  horizontally 24/7 at a little over 6 feet high.  Could that interfere with pollination on the higher blossoms?

It's too late for this year, but I need to try something different next year.  Ideas?

Boffer, YOU are asking for OUR input?    This has been a dismal tomato year for me. But, next year! There's always next year.

1. Don't know
2. 90* may be too hot for your tomatoes. Here, now that the temps are down in the 90's, I finally have 2 little tomatoes on a volunteer. I assume the ones you have outside are doing fine.
3. Does the fan dry out the blossoms more than they help with pollination. ? Tapping them early in the day before the fans are needed may actually be better.

I've read about tomato blossoms refusing to set at various temps ranging from 85 to 95 degrees, so 90 does fit in there.

Also read that early producers tend to have that problem more than late producers -- more sensitivity to heat. Dunno how reliable that is, can't remember the source, but I didn't discount it out of hand either.

Could hot air rising have anything to do with it? The blossoms at the bottom may be better shaded, and cooler. Some of my beefsteak tomatoes have only been setting fruit at the bottom, where heavily shaded from the sun by a cooling canopy of leaves. The ones on top are just drying up and falling off. It's only as our days have dropped from consistent 100+ temps that I'm getting a few tomatoes even a foot from the soil. The previous sets were only inches from the ground.

I'm having a similar problem with the newer fruit on my indeterminate tomatoes. In my case I am getting pollination but the fruit is slow to grow. I am chalking to up to the plant putting energy into the nearly mature fruit and I'm hoping the younger fruits will begin to grow once I begin harvesting.

how warm is the greenhouse at night?

http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/visual-guides/tomato-fruit-problems.aspx

Early on in the season, my tomatoes weren't setting fruit because it go too chilly for them at night. Their growth rate was OK, but the blossoms weren't setting. I resorted to misting the blossoms lightly with apple juice, and lightly tapping the clusters with a pencil. The apple juice emits ethylene oxide which promotes fruit setting and ripening, and the tapping dislodges pollen. Works for my tomatoes!

I hadn't heard about the apple juice trick.  Interesting.

The lower fruits would have been the ones experiencing cool night time temps, and they did OK with just my tapping the blossoms.  Our nights this year seem to be warmer than usual, around 60°.

Camp's link said that tomatoes need 6 hours of direct sunlight daily, but that's a rather vague requirement.  6 hours of Texas sun is a lot different than 6 hours of PNW sun.

I'd hate to be in Texas sun, then. We were over 100 like clockwork in July, but we tend to only get a little over a month of that here, thank goodness.