I think I know which sight, that you are referring to. Because the opening is much bigger, I think that's what makes it work. The farther from the eye, the larger the opening would have to be.
We just recently discussed this issue, somewhere, on this forum.
My recommendation, in that situation was to use the Johnson peep or take a long sight designed for the traditional Hawken and fit it to the barrel. In some cases the dovetail would have to be ground off the sight and drill holes to match the existing holes. Assuming that you did not want to modify the barrel.
I think Skinner Sights, has some sights that might work, however, it might need a taller front sight. But the Skinner, is a peep sight, but mounted on the barrel.