I must have been skimming through these first chapters pretty hard when i first read these years ago, since i missed the rather obvious innuendos on the first time.
Now after im rereading after the anime it's pretty clear that:
-In chapter 9 MC appears fuck Ru on the spot after she grew into her full size after the succ.
-Ru can't handle all the sex (He's too passionate)
-Why she stays as younger/smaller in c.10 is to avoid getting fucked as much, and she turns into a loli on noon as well to escape. Tia refers to this directly on c.12
-MC is not a lolicon(?)
-On last page of c.11 when tia is trying to flee as it's ''too much'', as she appears sweaty (if it's from sex or struggle to trying to flee), she is either intimidated from MC's excessive virility due his healthy body or is intimidated by MC's magnum dong. Either way she gets fucked.
-After c.12 (this one), the tables seem to have permanently turned on MC as the elves by themself as addition are enough to overpower MC in virility, and it doesn't get easier for him down the line either.
Thanks for coming to my Ted talk in near 5 year old comment thread.