To be honest i'm not sure which range marks are being refered to, i'm not much of a Salmon fan, LFN is my favourite.
I've always used the tactical display to gauge what the distance to target is then raise the attack scope once i'm in range. After that what i said in my previous post seems to work well enough for me.
Not being a simmer i rely more on my mk1 eyeballs rather than working out the angles. Some would call it guessing i call it experience
Maybe someone more experienced can clear up this diappearing range marks thing.