  We analyze how bound-state excitation, electron exchange and the residual
binding potential influence above-threshold ionization (ATI) in Helium prepared
in an excited $p$ state, oriented parallel and perpendicular to a linearly
polarized mid-IR field. Using ab initio B-spline Algebraic Diagrammatic
Construction (ADC), and several one-electron methods with effective potentials,
including the Schr\"odinger solver Qprop, modified versions of the Strong-Field
Approximation and the Coulomb-Quantum Orbit Strong-Field Approximation (CQSFA),
we find that these specific physical mechanisms leave significant imprints in
ATI spectra and photoelectron momentum distributions. Examples are changes of
up to two orders of magnitude in the high-energy photoelectron region, and
ramp-like structures that can be traced back to Coulomb-distorted trajectories.
The present work also shows that electron exchange renders rescattering less
effective, causing suppressions in the ATI plateau. Due to the long-range
potential, the electron continuum dynamics are no longer confined to the
polarization axis, in contrast to the predictions of traditional approaches.
Thus, one may in principle probe excited-state configurations perpendicular to
the driving-field polarization without the need for orthogonally polarized
fields.
