Q: When the GIRM says that the deacon should carry the book of the gospels “slightly elevated,” does that mean below the eyes?
A: I think that they chose a term that implies some flexibility. It probably mean to avoid holding the book way up high above your head, where it could appear taller than the processional cross, or too low, where it may appear too casual.
I think either above or below the eyes is acceptable as long as it is “slightly elevated”. They probably left it vague on purpose.