You're not understanding the point. If the Byakugan's wide range of vision is specified as an expansion of Neji's "ocular range", it means that it's dependent on his eye's ability to collect light from the surrounding environment (this time, his surrounding environment encompasses 360 degrees), "interprets" it, and transmits that signal through the optic nerve. The last part is essential information because Genjutsu is initiated through
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, which obviously, the optic nerve is a cranial nerve, so since Neji's Field of Vision pertains to the eye's ocular prowess, then he will succumb to Sharingan Genjutsu, regardless of whether or not his actual eye makes contact with Sasuke's Sharingan.