Let's see, for straight series some would be the teacher x students, like
Kodomo no Jikan or
Hoshihimemura no Naishobanashi, there's a continuation of this latter series. For loli yuri you can check
Itou Hachi and
Kugogane Ken, though this one is mostly a hentai artist. The author of the series I mentioned before have done more loli series, so check her out. More series about lolis MC would be Ryuuou no Oshigoto! (shogi), the author of
this work usually uses a full cast of lolis,
Saotome series has a nice legal loli,
Hachiko half of the times does onee-loli series but yes, from them it's mostly wholesome yuri. You have loli anthologies of Yurihime, Tanya the Devil (no romance though and not for all sensibilites/humour) and
Gochiusa (more wholesome yuri). Of course, there's isekai with genderbending with overpowered loli protagonists, but like Tanya the Devil they're dudes inside.
So, in short, ecchi loli series with the loli as MC are scarce, since they prefer to turn them on hentai and well, there's not much plot there, leave them wholesome or make the lolis secondary (because brain-deads and bigs boobs sell better). I just hope you had some of this series yet to be read.