  Experiments have shown that self-propelled particles can slide along the
surface of a circular obstacle without becoming trapped over long times. Using
simulations and theory, we study the impact of boundary conditions on the
diffusive transport of active particles in an obstacle lattice. We find that
particle dynamics with sliding boundary conditions result in large
diffusivities even at high obstacle density, unlike classical specular
reflection. These dynamics are very well described by a model based on
Run-and-Tumble particles with microscopically derived reorientation functions
arising from obstacle-induced tumbles. This model, however, fails to describe
fine structure in the diffusivity at high obstacle density predicted by
simulations. Using a simple deterministic model, we show that this structure
results from particles being guided by the lattice. Our results thus show how
non-classical surface scattering introduces a dependence on the lattice
geometry at high densities. We discuss implications for the study of bacteria
in complex environments.
