I haven't found a picture of a higher front sight yet but did find this picture of an 1860's hammer top and notch that's been deepened considerably.
Post #19 describes the process and results:
Here's a pic of an old Navy with a different front sight. I've seen several in the same museum (bbhc.org) with similar front sights, a very small dovetail. You have to look cloesly at the pic to see it (upper gun in pic). I guess the guy that had it wanted it to hit right on point of aim.
I have an original 1851 Navy Colt made in 1862 that has the same blade front sight as the 1860s. Research shows that there were many variations of sights that came out of the Colt factory. Blade front is one.