On inequalities between norms of partial derivatives on convex domains

We consider inequalities between $L_p$-norms of partial derivatives, $p\in [1,+\mathrm{\infty }]$, for bivariate concave functions on a convex domain that vanish on the boundary. Can the ratio between those norms be arbitrarily large? If not, what is the upper bound? We show that for $p=1$, the ratio is always bounded and find sharp estimates, while for $p>1$, the answer depends on the geometry of the domain.