I have no opinion on the rights or wrongs of the OP or the radio guy, but wonder, if you are making an approach to land (with or without PPR) to a field with this type of comms coverage wouldn't the default (and safer) join be from the overhead regardless if preceding and/or local traffic are joining in other ways. Why would you join on base like the OP did, is it personal choice i.e. just however you fancy joining coz its uncontrolled or would the AG guy offer this join?
Never been to Popham and no idea where it is, just trying to figure out the correct procedure for this type of field and setup, if indeed there is such a thing.