The mount plate I have (and that guy HAD) is see through so you can use open sights if you want. I think this elevation contributes to not being able to sight mine in without inserts.
I was not aware of that,but the simple fact is that any type of see through mounts place the scope too high above the boreto obtain a proper zero withsome scopes as well as being too high to achieve the proper cheek position on the stock.They also prevent proper bore sighting.