Here's a rather interesting analysis of the Tiger's commander's cupola by British tankers. It's no secret that the British weren't huge fans of German observation devices, but here is a pretty thorough list of its deficiencies, backed by a handy diagram.
As you can see, the Tiger has a pretty sizeable dead zone (30.5 to 36.5 meters) to the right and rear-right due to the position of the commander's cupola, which the British comment on as being an effective approach for infantry with anti-tank weapons.
Let's compare this cupola to that of the KV-1S tank.
Despite having a cupola in roughly the same place, the dead zone to the right and rear-right is only 11-14 meters, less than half as much as the Tiger. The KV-1S also sees slightly better to the left and rear-left, with a dead zone of 9-11 meters to the Tiger's 12-15. The KV-1S has worse vision forward though, a dead zone of 28 meters compared to the Tiger's 18. The field of view is also obscured by the gunner's periscope, which the Tiger does not have. On the flip-side, the Tiger's gunner is restricted to the narrow field of view of his gun scope.