I don't see why it's not okay. Where I see how it may not be ideal is that you'll have to ensure you're digging around those crevices to get your mash stirred well. I can see how pockets of dough can form and you may find you'll end up with lower efficiency. It's just a guess.
Frankly, I don't know if there is anything to the shape of a MLT. Not that it means there isn't, I just don't think I've come across any information yet that suggested otherwise. Of course, I haven't been looking either, so this is all a matter of opinion to me.