For canon characters with alters... I think Chuuya has one Verlaine that acts very differently from the actual one, probably formed around when the first met and based off the limited info Chuuya knew about him. Because of this he's very silent, angry, and destructive, it's not ideal for his system but it works in my mind.
I think Sigma would in canon have a Fyodor introject based off the 'bad' side, but also she could have a caregiver version. I think that would confuse her especially if this Fyodor introject was very nice to the rest of the system as well and can be found in headspace baking cookies.
I would say that the Mori alters that Yosano and Dazai have are similar to the Sigma situation, or else they're heightened to be 'persecutory' (if that makes sense).
Dazai maybe also has an 'ideal' version of a few people, while I'm thinking of Ranpo, the side that can solve any problem and do everything which is unlike the real Ranpo who is more of a nervous wreck (although he hides it).
Ranpo Fukuzawa alter could also be interesting. Again, very idealized and more physically caring than the canon Fukuzawa- Possibly acts in a way that Ranpo subconsciously wants more from his father figure.