Yes, but a new comment doesn't immediately sink five places, unless the comments above it are very highly upvoted - or the comment is very large. That is, there is a grace period that keeps a comment on top of a thread for a little while, presumably to give it a chance to be read. But, I've noticed that large comments are automatically pushed down into a thread so the grace period for them is much reduced (and probably weighted by the size of the comment).

That's not absolute, because I remember it stated elesewhere by dang that larger comments are considered more likely to be more substantial (for sound reasons). But it seems that holds up to a certain point. There is probably some kind of comment size range, of maximum and minimum comment size, outwith which a comment is pushed down.

There are other factors, also that cause a comment to automatically sink. For example, I have the (admittedly very bad) habbit of editing and re-editing my comments over and over again. I've noticed that if I do this in a sufficiently large comment, the comment immediately sinks when I refresh the thread page after an edit. If the comment is smaller, it can take quite a bit more editing. I think this behaviour is also weighted by user karma or time since account creation because my comments started sinking less often as my karma increased. Or maybe the rules of the site changed in the meantime.

Bottom line: large comments with some edits sink like lead.