FootprintOverlapDetector Detection Problem

Greetings dear Orekit Community,

Recently, I’ve been working with satellite detection and crossings through some complex regions-of-interest such as countries. Thanks to the valuable discussion made here and the great code example shared by @lghizoni, I have managed to adjust myself a complex region and a satellite detector. While GeographicZoneDetector works perfectly fine, I am having some trouble with working FootprintOverlapDetector.

Inside the FootprintOverlapDetector, @lghizoni defined a FoV with the following lines of code:

# Instrument Field-Of-View
swath = 15.0 # km
xfov  = degrees(atan((swath/2)/(ra*1e-3)))
yfov  = 30.0 + xfov
fov_margin = 0.0

Here in the xfov variable, entering say, 500000 meters to the apogee value yields something around 0.859372 degrees which is really small. And running the event detector with this xfov value, no satellite crossing is detected whatsoever. I am suspecting that above code should be revised in someway, but not sure. Perhaps I am creating a very small FoV and it just does not pass the region?

I am also confused with the the yfov line. Why 30 degrees is added to xfov?

Any discussion will be much appreciated. Thank you in advance,