You absolute GoaT. Most of the games I can think of are already on the list. It's a sad affair for us who like small breasts without it having to be loli. Not much out there it seems. There might be some hope with the creators of Detective Girl of the Steam City, or some other eastern game studio.
I have some games that might be added to the list but sadly I can't provide the tags since I don't remember that much about them (just that they had mostly small breasts). The last time I played those (or any adult game for that matter) was in early 2020 (yeah, the first months of the pandemic gave me time to try them).
Small:
* Lilith's Throne: While some of the main NPCs are big breasted and too furry for my taste, the cool thing with this game are the heavily customizable procedurally generated NPCs, of which you can capture an infinite (?) amount. Last time I played it was mostly a text game though, like, there's some sprites for the clothes the characters are wearing but it provides you text descriptions not CGs. That's the price to pay for having a flexible sandbox and a ton of freedom.
* Corruption of Champions II : Similar to Lilith's Throne.
* The Imperial Gatekeeper: Just like Lilith's Throne, there's all kind of body-types. I just chose to focus on the ones I liked, of which there were plently since they are procedurally generated and with good art.
* SuperDeepthroat: Another hyper-customizable one.
* Sanguine Rose: It's actually just one of the characters (the half goblin girl), but there's only a couple of characters you can have sex with in this short VN anyways.
* Monster Girl Club Bifrost: Same thing, there's all breast sizes in this brothel management game, so you can focus con what you like.
* Brothel King: This is (was?) another brothel management but it was very customizable because you straight up provided the images for the from your personal H folder (or community made packs).
* Virgin Invader: Most tend to be small or medium.
* Sengoku Rance: There's variety, with a good amount of small.
* Eiyuu*Senki: The World Conquest : Similar to Sengoku Rance.
* Poke Abby.
* Short Butt Sweet.
* Katawa Shoujo.
* D.P: NTR alert. Not CG just very limited pixel animation.
* NTRPG 2 : Same as D.P.
* Henteria Chronicles Chapter 1: The Lady and the butler : Same as D.P.
* PIXXXEL #002 Fam*liar of Zero Lou*se / Si*sta / Henr*etta : Very short VN with good pixel animation.
* Brave Alchemist Colette : You can toggle either huge or small breasts for the main protagonist. It's kinda like Detective Girl of the Steam City but medieval fantasy and sadly with many grotesquely big boobs around besides the main chara and a random futa scene at the start.
* Utawarerumono: Played it eons ago so can't remember much but IIRC all the girls are small breasted.
* Leane 2: Leane of Legitimate Crown: If you like NTR, the scenes from this game are godly (and they have audio). The game genre is kinda 4X strategy which might or might not be your cup of tea, but I love the genre and... I thought the gameplay was very bad. One of the few times I downloaded a savefile just to play the H-scenes.
Medium:
* Witch Trainer.
* Princess Trainer.
* Star Channel 34.
* Four Elements Trainer (haven't played the Toph chapter yet, that might qualify as small).
* The Wind's Disciple.
Not sure:
* Something Unlimited: Sadly with each update the new girls (and the new CGs of the old girls) started having bigger and bigger breasts, and it was kinda on the limit for me to start with (I was just willing to overlook it because of the appealing power fantasy).
