in my opinion, you should never paint in the eyes. go look at anyone around you on the street and try to figure out how close they have to be before you can make out any details about their eyes. then notice how big their head looks compared to a 1/35 scale head held about 1.5 feet away from you (typical viewing distance for a model).

unless you have the eyes of a hawk, you won't see whites of anyone's eyes till they are quite close and appear far larger than that 1/35 scale figure at 1.5 feet distance - especially outside in daylight (even a cloudy day) when people are squinting (daylight is also the assumed case for most military figure presentations).

painting in eye detail on such a small figure is futile and unrealistic as far as i can tell. not painting in eyeballs and instead just giving the area a dark wash is easier and more accurate.

but then again, people like a challenge in this hobby...

nice enough work for your first try with oils though - better than my shaky hands can manage (hence my "you can't see people's eyeballs most the time" justifications)