Radio is also one to many, inherently.
And you can do social engineering head games with counter intel officers. Send 37 distinct repeated messages one day... that would seem to strongly imply 37 individual agents, but in reality you could have anything from 0 to 1000. OTP message #24256 might be heard by field agents 351 938 and 271 and it means "check your dead drop signal". One agent sees a chalk mark on the street and gets a real message at his dead drop, the other two see nothing and chill. OTP message 91053 could mean "unrestricted warfare begins tomorrow at noon" for all 1000 agents, perhaps. Or maybe OTP message 91053 means nothing, nothing at all and its all head games for counter intel.
There are also chain strategies such as I own a "suspicious" shortwave radio and listen to it (which in some parts of the world that are not USA, is not unusual or suspicious) and when I get OTP message I am to offer my collectible Dale Earnhardt mint condition collectors plate for $1599 on ebay. The agent who's actually doing something interesting is a well known 90s nascar fan and when he sees my collectors plate offered for $1599 on ebay when the going rate is $5, that's when he steals the secrets or pushes the button or whatever. I listen to shortwave which means I could be a spy but all I ever do is try to sell junk on ebay, whereas the "real" agent is an indistinguishable nascar fan.
There are protocols using OTP where the metadata could quite easily give away an agent even if the data is never cracked even with the rubber hose technology. For example imagine a really bad protocol of page number, word number. Won't take long to figure this out when the first number increases at a predictable rate never exceeding 351 pages and the second number never exceeds the number of words on a page. All you need to do is have customs record the number of pages in each book travelers import, and when you figure out the pad rotates at 351 pages you find the guy who entered the country with a 351 page book, and do absolutely nothing other than alert customs to record the exact name and edition of every book he has ever or will ever import, at which point you now have a copy of his one time pad. That's a horrible protocol that uses OTPs, but its hardly the only crackable one that exists.
Personally, given how incredibly cheap it is to transmit numbers over the radio, and how incredibly expensive it is for counterintel to try to figure it out and track it, even if it were obsolete 20 years ago, I'd still keep doing it as a pure economic attack. That counterintel agent listening to numbers is one agent who's not inspecting the contents of suspicious looking icmp packets or multiplayer video game conversations or funny chalk marks in front of libraries or whatever.