Back before I started growing only single stem tomatoes I found that a free growing plant that isn't pruned will produce too many stems and too many blossoms and set a far lower percentage of fruit than a moderately pruned plant. Try taking out most of the suckers and opening up the plant some and don't allow more than 4 or 5 stems. Made sure to give the plant plenty of water during the heavy blooming stage. It sounds to me like you could just have plain old blossom drop which can be caused by too little moisture, too much moisture, and too many growth tips competing with the flowers. It can also be caused by disease or pests but since you didn't mention them I assume the plants are healthy.
The temperatures you describe sound great for most varieties and your humidity sounds lower than what I have to deal with usually so those two things shouldn't be hurting blossom set.
Bill
|