i think it requires the right amount of cover and trying again.
my PK gal freaked out and stressed so bad when i first put her in her 2 gallon, that she got ick.
did it again when i tried out the 1.5
i, like you, thought she liked her one gallon, over a bigger tank.
but, i tried it again, putting more plants, and now she lives happily in her 2 gallon. the problem may be, you didn't add enough plants. tall, short, floating.... enough plants, and he'll be happy. baffling the filter might help, too. HMs tail bite if they can't handle the current.