Depends on what you mean by mixing. If you mean characters who are both muscular and fat, ie "strongfat", I'm not entirely opposed to it and have a couple of characters who lean that way, even if I haven't drawn them particularly often. There's a few reasons, chief among them that I don't think I'm particularly good at drawing it yet; I get too focused on one aspect or the other and it ends up feeling off, imo. I'll likely try and work on that in the future.

If you mean having muscular and fat characters interacting, that's also not something I'm opposed to at all, and likely one of the reasons I hadn't really depicted it is because I had made the decision to separate the "main" and muscle-focused twitter accounts to try and keep things separate out of some worry that not doing so would upset people. I've since undone that because I don't WANT to keep things separate, and in fact the next story after this Excess one will have some amount of focus on that.