Adjoint action of automorphism groups on radical endomorphisms, generic equivalence and Dynkin quivers

Let $Q$ be a connected quiver with no oriented cycles, $k$ the field of complex numbers and $P$ a projective representation of $Q$. We study the adjoint action of the automorphism group ${\text{Aut}}_{kQ}P$ on the space of radical endomorphisms ${\text{radE}}_{kQ}P$. Using generic equivalence, we show that the quiver $Q$ has the property that there exists a dense open ${\text{Aut}}_{kQ}P$-orbit in ${\text{radE}}_{kQ}P$, for all projective representations $P$, if and only if $Q$ is a Dynkin quiver. This gives a new characterisation of Dynkin quivers.