> Let $\mathcal{A} \subset \mathcal{K}$ be two locally presentable
> categories. $\mathcal{A}$ reflective and closed under filtered
> colimits. Then $\mathcal{A}$ is a small-orthogonality class. Let
> $R:\mathcal{K}\to \mathcal{A}$ be the reflection. Let $G$ be a dense
> generator of $\mathcal{K}$. Can we conclude that $\mathcal{A}$ is the
> small-orthogonality class with respect to the set of maps 
> $\{\eta_g:g\to Rg \mid g\in G\}$ ?

I think that the answer is negative in full generality and I would like to see a counterexample.