Just wanted to update.
I ended up adding a small Watanabei female to the tank and have had excellent success. Their first interaction was amazing. They swam to each other immediately, greeted and checked each other out then swam side by side throughout the tank. They are both out and about all the time. He some times does the super fast charge at her and chases her for a second or two. She hides for 30 seconds then comes back out of the rock work. No fear or damage. IME, overall their interactions are not hostile in any way.
I am enjoying this pair immensely.