  Ballistic, gate-defined devices in two-dimensional materials offer a platform
for electron optics phenomena influenced by the material's properties and gate
control. We study the ray trajectory dynamics of all-electronic, gate-defined
cavities in bilayer graphene to establish how distinct regimes of the internal
and outgoing charge carrier dynamics can be tuned and optimized by the cavity
shape, symmetry, and parameter choice, e.g., the band gap and the cavity
orientation. In particular, we compare the dynamics of two cavity shapes,
o'nigiri, and Lima\c{c}on cavities, which fall into different symmetry classes.
We demonstrate that for stabilising regular, internal cavity modes, such as
periodic and whispering gallery orbits, it is beneficial to match the cavity
shape to the bilayer graphene Fermi line contour. Conversely, a cavity of a
different symmetry than the material dispersion allows one to determine
preferred emission directionalities in the emitted far-field.
