The obstruction of a reflector is defined by the size of the secondary mirror. That size depends upon the optical design of the telescope. The shorter the focal length of the telescope the larger the obstruction.
Some companies however present the numbers a little different.
Some others only give the diameter of the secondary mirror and not the diameter of its support. It's pretty clear that this changes the numbers pretty much. The loss of light corresponds with its surface obstruction. Even with large obstructions, the loss of light is little. This means visually the difference is barely distinctable.