My pair of Pearl Gouramies used to be shy in the beginning, when they were sick (anchor worms). Since I got them clean and happy, they have gradually lost their shy behaviour. Now they will come and eat from the tweezers, with the light cover angled upwards and my hand over them. This used to be unthinkable.
So what I am thinking is that they might not feel well, either being stressed by disease, water condition, or other - faster - inhabitants. They are kind of slow and easy to scare, but mine are now always around, mostly on the surface, looking for anything edible, like algae and dying plant parts. The dense vegetation seems to give them some confidence.
I started with that pair in my 100 gal thinking I would add more if they'd make it, but they seem to be very content with each other. I can see how two or more males would be fighting, and more females could be good, but being big fishies they fill in the tank.
Here's another thought before I really shut up: perhaps they need to see some big fishies that are not scared to loose their shy behaviour. I have a pair of butterfly fishies, they always come to the front when I show up, and now some loaches that are all over the place... maybe that tells them that there is no danger in coming out to the front and top.
Also I have a lot of plants floating on the surface, Riccia, Utricularia, Water Sprites, Myriophyllum, perhaps that helps too, vs a naked surface with PC's blasting down on them :shock: