Something I was told a long time ago for easier eyes was to paint them looking to the side. It prevents the troops from going cross eyed, and makes cleanup with skintone a lot easier. It also tends to make them look more dramatic.

With helmeted Cadians, rather than doing eyes, an option is to put them on their back, feet slightly elevated and drop some brown or mixed brown-black wash to the eye area. It will dry looking like helmet brim shadow.