update
after a couple months I found the pair to be incompatible....
I was feeding the butterfly some crickets when the leaf fish slowly starting inching its way towards him. The leaf fish struck then struck again, greedily not allowing the butterfly to eat. In the wild (in which these two would never be together) the ABF could easily out-swim the slow, stealthy leaf fish, but in 20g long there was nowhere to go. The next day I made arrangements to transfer the butterfly to a friends tank where he remains to this day.
On another note Ive found the specific leaf fish to be dominant and territorial (unlike the first one I had.) So my first attempt to incorporate more leaf fish into the tank ended in failure. I bought a single specimen and introduced him into the tank. Within a few hours the original was swimming the length of the tank, back and forth, pausing only to flex his jaw like a mighty roar. When roaring he would angle his head down, fully extend his mouth out like a yawn and shake back and forth. Quite interesting I assure you
The new recruit died within two weeks, Im assuming from stress.
My next attempt involved introducing two leaf fish to break up the attention. The new duo and I got treated to the same display of pacing and roaring, yet they managed to secure some territory (not quite the prime real-estate of the tank) on the right hand side while the dominant one held down the good spot on the left. Surprisingly, sometimes I would see two fish on the left side, basically hangin out with each other... it was kind of weird. Yet within a month one died. Now I am down to two. I have rearranged the tank to be leaf fish friendly with the "island layout" consisting of a huge rock, a piece of driftwood, and large leaf silk plants. As of today, the two still stick to their own sides but now both sides have good cover.
Well, thats where Im at now, and things have been stabilized for about a month. The lfs' that sell leaf fish have been out of stock for a while, but Im considering trying to introduce one more in the future. I dont know, we'll see.
Just thought I'd update, questions and comments welcome.