The damage threshold is given in the datasheet for the sphere inner surface rather than for the detector itself, because the sphere surface will reach its damage threshold long before the detector will. A beam entering the sphere will first hit the inner surface on the opposite side of the sphere, and if at that point the power density is too high it will damage the inner surface of the sphere. From that first "meeting" of the beam with the white diffuse reflective inner sphere surface, it will be diffusely reflected multiple times. Since there is no direct line of sight between the entrance port and the detector, any light reaching the detector has already been uniformly distributed around the inner surface of the sphere, but light in that "first impact" on the sphere wall has not yet been uniformly distributed. Therefore, the "damage threshold" for the device is the maximum power density of the beam as it first hits the inner wall.

The IS6-D type integrating spheres (such as IS6-D-VIS, IS6-D-UV, IS6-D-IR) will be good for this as long as you orient the 80 degree divergence in the vertical direction. The IS1.5-VIS-FPD-800 will also work, with the same constraint.