i f you reduce the size of the face, it should not be a problem. by properly shaping the graver, the face is reduced well below max. one good reason for this, touchup is much faster as there's way less metal to abrade away. also, the larger the face, in your case, more face to visually distract you.
chemistry: the various acids, bases and and slew of "stuff" that makes work easier as well as better looking. also, electro etching with salt water. the process is dangerous as chlorine gas is released. safety first, kids !
i forgot to mention the brass is very thin. that's why one should put protective bags inside the instrument. it can prevent unwanted dimples here & there. look up "jason" saxophone engraver. his vid is spot on. sorry, his name is jason du mars. a careful look at his video will show some...
first order of bizzness: you must figure a way to safely cradle the sax. all the keys must be protected from damage. 2nd: go to yer local junkyard. get a couple brass lamp bases-- and practice the "wriggle" cut. 3rd: make bags of rice, sand, or whatever to protect the instrument whilst...
are you certain that the objective is seated properly ? if the objective is off axis a bit, such could be the problem. is the prism loose ? crazy little things can cause problems.
you're correct. cermark does just that. i u don't know where it'ss made now.se it for finished products. i've never used it as a layout for hand engraving. i do think it would worrk for layout and subsequent hand cutting. cermark used to be manufactured just a few blocks from my house.