You can see the antennas on the PCB at https://docs.gl-inet.com/en/2/hardware/ar300m/#pcb-pinout
The are cross-pol, which is good for diversity, generally increasing robustness of connections over the covered area. Being physically small compared to the wavelength at 2.4 GHz (~12 cm) there won’t be much directionality to the pattern, as kyson-lok indicates.
I would suggest not placing the router on or near (under ~10 cm) a metallic or conductive shelf or object, with ~30 cm potentially being better. RF can be very non-intuitive, so checking the signal strength where it matters to you is the best way to see if “tweaks” in location help or hurt.