RE: Bid17 Jun 2021 16:36
It's generally not the MMs doing it: this is a SETS share where the prices are set by a stack of orders bid and ask sides in an electronic book, matching bid and ask orders (those are the A trades). The bid price is just the price at the top of that stack, and the ask is the top of the other. (There's an electronic auction period at the start and end of the day, but that often doesn't do much either.) The MMs generally keep away from the action, further down in the book.
In short, some traders are setting things up, I think to force the price of O trades, which are off-book and (usually) with the MMs. There isn't a lot of volume in the book itself. From time to time I try trading in it, but it's hard work, and sometimes one of the bots insists on setting the price by jumping over anything I put in. So I've mainly left them to it.