  This article investigates the approximation quality achievable for
biobjective minimization problems with respect to the Pareto cone by solutions
that are (approximately) optimal with respect to larger ordering cones. When
simultaneously considering $\alpha$-approximations for all closed convex
ordering cones of a fixed inner angle $\gamma \in [\frac \pi 2, \pi]$, an
approximation guarantee between $\alpha$ and $2 \alpha$ is achieved, which
depends continuously on $\gamma$. The analysis is best-possible for any inner
angle and it generalizes and unifies the known results that the set of
supported solutions is a 2-approximation and that the efficient set itself is a
1-approximation. Moreover, it is shown that, for maximization problems, no
approximation guarantee is achievable by considering larger ordering cones in
the described fashion, which again generalizes a known result about the set of
supported solutions.
