Not really much point to this post other than to validate the parents who struggle with feeling beholden to birth parents. Ive read several posts about 'towing the line' with letter box contact due to the agency suggesting that rocking the boat may lead to BPs withdrawing from the agreement and feeling like it's all set up in BPs favour. I'm currently doing a piece of work with some BPs (an interesting insight for me as someone who is planning to apply to adopt soon...haven't told them that but) and guess what...they say exactly the same thing!! Their child was placed for adoption several years ago. There are some parts of the letters that they find very difficult but if they raise it with the agency they are told not to challenge it as APs could decide to stop writing the letters.
No real point to this post but it was a bit of a light bulb moment as what they were saying was the same as what I've read a lot of people say on here so thought it might be of some small consolation to know that the feeling is mutual on the other side!