The 3/4 inch height worked OK except for empty flat or well cars. As the instructions had suggested, there was no problem at all with the spaces between cars using the angled arrangement.
Thinking about how the lateral angle was used to prevent the signal from passing between the cars, I thought that using vertical angle as well could help
This worked the best with very few instances of the signal getting around or through any of the cars in the test train.
This photo with the IR beam path drawn in shows how the sensors could be installed on the approaches to the grade crossing.
The Azatrax IR detection circuit seems to work very well and come in several configurations. To learn about what is available check their website.