To breed my veileds, I always show the female to the male
by holding her outside his cage on a branch. If she is receptive
(doesn't hiss, doesn't gape, doesn't sway back and forth, and
doesn't darken her background color but remains calm, etc.)
and the male reacts in a suitable fashion to her (tail not
curling and uncurling, not gaping or hissing, not holding one
"hand" up close to his chest...but is calm and starts to approach
her)I put her inside his cage. If either of them reacts
negatively/non-receptively I wait a few days and try again.
I have heard of the odd male head-butting the female without
causing harm to the female...but none of mine have ever done it.
It might be part of the "ritual" for some males...I'm not sure.
I have always put the female into the male's cage just because
that's what I heard was the way to do it and since it always
worked, I never tried it the other way around. I also find my
female to be easier to move from one cage to the other than some
of my males.
Hope this helps!