"on the second visit I was given a very hostile reception by immigration"

In other words, the immigration officer did his/her job and questioned why you were traveling in an unusual pattern? They were doing their job. Provided that you have a valid reason to be there and can show this, then you shouldn't worry about it. They very well may question you, but that is their job. You shouldn't take offense to that and it is not a hostility. They do catch people doing things they shouldn't occasionally you know.