That's pretty natural, all in all. Saki seems to be the one the least affected by the bonobo genes, perhaps because she might be the one thinking about it the most (and consequently fighting against such a legacy). So, even though she seeks comfort from the only source available when Shun isn't there for her, it's not like she'd necessarily want to be with Maria intimately, so she couldn't really be in control. On the other hand, there's no way Maria wouldn't realise how Mamoru feels, but it looks like she's just enjoying torturing him, so it fits well together with being the dominant one as well with Saki.