I have not aware of any wifi radiation patterns published by GL.iNet for their routers. With the external antennas on the Slate, I expect that router has an omnidirectional pattern radiating horizontally when the antennas are pointing up. With the internal antennas in the Creta, I expect that router has an omnidirectional pattern radiating horizontally when the device is positioned vertically and the printing is oriented normally. If so, then the router should be location centrally within the area covered.
I bought the Slate only as a travel router, so it is not so important to me. In comparing the signal strength between the Slate and my TP-Link home access point at different home locations, the Slate is much weaker than the TP-Link.