When you self-reference an entity in the domain model, the association is barely visible and hidden behind the entity itself. This makes it difficult to a) get a clear picture of all associations and b) work with/update the association from the visual representation of the domain model.
My suggestion would be to display self references with a circular line to itself. Alternatively, use the same method as with the lines in microflows where you can drag to set 'bezier' points.
Mendix 7.23.6 has been released and it greatly improves the readability of self-referencing associations! Also, cardinalities (1, *) are drawn on the line instead of next to it, also helping readability.
I have a dream that this will be implemented one day.
In Mx7.18.1 you can edit the reference from the association tab. So at least you now can more easily change / check the settings.
I posted the same idea months ago, but it seems no one from Mendix took a look at it: https://forum.mendix.com/link/ideas/789
Hopefully they see it this time.