Okay, here's what I have observed.
When the birds are on the chicks, Smiley has his left wing tip over his right. Princess is just the opposite, right over left.
Princess hunkers down while on the nest, Smiley is more upright, sort of like an on guard pose.
When you can see them face on, Smiley's malar stripes appear squared off and rectangular while Princess's are more rounded.