Hyper is always the highest stage of spell you can cast; but it is intended for fertility of some characters to improve with story progression. This is already shown with Full Moon but other story beats will mimic that progression of enhancing a batch of maiden's fertility and giving them larger than typical sizes. This enhanced size after story progression is the intended limit I have planned, so if you've seen Full Moon then you've seen the intended limit, and more characters are planned to reach that limit or surpass it but not by much.