[abgar]

Try inverting the start and end radius?

new Float:vec[3];
GetClientAbsOrigin(client, vec);

vec[2] += 10;
TE_SetupBeamRingPoint(vec, 100.0, 99.0, g_BeamSprite, g_HaloSprite, 0, 15, 1.0, 5.0, 0.0, {0, 0, 255, 255}, 10, 0);
TE_SendToAll();

This has worked well for me in the past.
Also, depending on what HaloSprite you're using, will change the effect and the 'cleanliness' of the ring