One thing to remember on the 545/546 stamps, along with 595 on the next Bureau series, are that they are notoriously centered badly, because they were so wide.
Harder to tell on a screen but the rotary 1c greens, at least to me, tend to be lighter, and the flat plates tend to be darker. This stamp just looks more like a flat plate stamp to me...I may be way off though.

Here are from my collection, a 424, 545, 546.
The 545 looks different than the flat plate 424, and there's barely enough room for the image on the stamp on the 545.
Can't give you a good reason for the measurements earlier, but thought I'd chime in. It really looks more like a flat plate stamp to me. I've been wrong before, lots of times! :)
Ray