  Magnetic pair creation $\gamma \to e^+e^-$ has been at the core of radio
pulsar paradigms and central to polar cap models of gamma-ray pulsars for over
three decades. The Fermi gamma-ray pulsar population now exceeds 140 sources
and has defined an important part of Fermi's science legacy. Among the
population characteristics well established is the common occurrence of
exponential turnovers in their spectra in the 1--10 GeV range. These turnovers
are too gradual to arise from magnetic pair creation in the strong magnetic
fields of pulsar inner magnetospheres. By demanding insignificant photon
attenuation precipitated by such single-photon pair creation, the energies of
these turnovers for Fermi pulsars can be used to compute lower bounds for the
typical altitude of GeV band emission. This paper explores such pair
transparency constraints below the turnover energy, and updates earlier
altitude bound determinations of that have been deployed in various Fermi
pulsar papers. For low altitude emission locales, general relativistic
influences are found to be important. Rotational aberration influences are also
explored, and are found to be small at low altitudes, except near the magnetic
pole. The altitude bounds are typically in the range of 2-7 stellar radii for
the young Fermi pulsar population, and provide key information on the emission
altitude in radio quiet pulsars that do not possess double-peaked pulse
profiles. The bound for the Crab pulsar is at a much higher altitude, with the
putative detection by MAGIC out to 350-400 GeV implying a lower bound of 310km
to the emission region, i.e., approximately 20% of the light cylinder radius.
These results are also extended to the super-critical field domain, where it is
found that emission in magnetars originating below around 10 stellar radii will
not appear in the Fermi-LAT band.
