You can look at this link to the wiki which measured gap..
I use a Mergress and a 38C, and they just feel different against my face. I can't look at them both side-on right now to see if the head radius is different, but will comment when I do. I use the Mergress from about 2.5 to 3.5 during different passes and feel that it brackets my 38C.
Understand that this table is not to be taken as gospel, but more for general comparison. As I have followed comments in this forum, many indicate that a model that measured as having a lesser gap is more aggressive in their version/hands.
Thats if you look at "5" being the top of the scale. It is very useable and the blade is still tight in place to use it at the "12" setting. That is what I use every time. For me the "5" by comparison is a mild setting.
Yes, this is assuming you use "5" as the top of the scale. I have never tried doing another full revolution if that is what you are refering to 12 as, since my knob goes from 1 to 5, . I'll go with the setting in jrhudgin's reply and say for me 3 to 3.5, since the original post was comparing the progress adjustment to the HD