There is no spec for distance as it all depends on the scenario. What matters is how well the wireless signal can travel. What barriers are there to block the transmission and what other electronic equipment is around that might interfere with the signal.
I had scenario where we had to put access points only 20 feet apart because the interveneing space was a steel and concrete stairwell that just stopped the signal cold.
I had another were the signal worked fine hundreds of feet away because the area was an open warehouse shop floor.
If your laptop is only one standard indoor wall away from the SSG20 then you should readily get a good 75-100 feet. Unless there is a source of interference in the area.