I see there are comments on the 1.9.5.5 bug list re: intelligence agents getting caught with extreme regularity. This has happened to me over past three games, maybe 75% steel territory map missions ending in capture on advertised ~90% success chance.
Try sending your agents out for 3 months instead of a year, if the reduction in base chance isn't too bad a tradeoff. Might be that you end up with 1/4th the chance to be detected by ongoing counter-espionage.
I've had pretty good luck with that, but I haven't done extensive testing.