When I still had my "studio" set up, the black velvet background was typically about 3'-4' behind the flowers, I had reflective umbrellas set up at about 45° angles on either side, and a small, white reflector positioned slightly behind the flower to give a very small amount of backlight.
Here's a few examples....maybe not the best.
Paph. Annabellchen
Phal. Mituo King
Paph. Margie Goward