1:10? Never heard of it.How can you tell that the small tank didn't affect them in any way? Usually 10gallon tanks are 15-17 inches long, just three times longer than an adult pearl gourami. Afterall, they live up to 8-10 years and are potentially aggressive.
A good basic rule is to make shure that the tank is 10 times as long as the fishs's body length. Imo the minimum tank size for pearls is 45-50 gallons.