Mate I've been using this constantly but just realised I was using it not quite as you describe here as I don't pay attention to the position of the fixed letter. I now realise this doesn't really make sense, ha!
I pick one letter of the word which forms the 'base' of the new word. I pick another letter from the word and use it in any position before or after the base letter, until I see a new word, regardless of the base letters original position. I think it allows for many more word possibilities but I understand now it diminishes the puzzle aspect and compromises its purpose a little. I'm going to try it properly.