For testing how about placing the sensors so that something could fall between them like a piece of paper of a known length possibly with 2 coins taped to the bottom corners so that the paper falls pretty much straight down. You can then drop the paper with the bottom edge just above the sensor and then have it time how long it takes for the the paper to pass through the sensor.
Then you can use d = 0.5 * g * t^2 to calculate how long it should take and compare it to the results from the script. For example a 1 meter long piece of paper (which is probably really too long to give good results because of drag). The time to pass would be approx. .452 seconds.
Just an idea, I do not know how realistic or how reliable the results will be.