Well formedness of Associated data type

[fxdpntthm]

Currently we assign a mirror $wf:ATC to an associated type ATC of class say C.
or

class C  a where
   type ATC a 
   op :: ...

gets elaborated to

class C  a where
   type ATC a 
   type $wf:ATC a :: Constraint
   op :: ...

Will it be more appropriate to add the class constraint as the wellformedness mirror?

Possible problem may be that the associated data type has fewer type variables than the class variables potentially, giving rise to unambiguous types post elaboration.

Motivation:
There are cases where a data type references an associated type.

data IsNode a => Graph a = Graph { graphMap :: (Map (Key a) a) }

class Ord (Key a) => IsNode a where
  type Key a :: *
  nodeKey :: a -> Key a
  nodeNeighbors :: a -> [Key a]