I got lucky and was able to talk my girlfriend out of an old pair. A compressor can also help with sibilance when used properly. Again, I personally try to do everything with as little processing as possible. There are over 100 places inside the human head and nasal passages to place the voice when singing and speaking. Some are more nasally and some may be more throaty.
Every singer has their own way of getting their voice out of their head.
A singer's tone is as unique as a finger print. It is your job as a recording engineer to find the best qualities of their tone and capture it. Their are no rules for mike placement. It doesn't matter how close or how far you put the mike from the singer's mouth. All that matters is that it sounds good.