Bartian, that is exciting news … i f… the fish are really P. sumatranus. But I doubt it. Even sumatranus have a very small filament in the caudal fin, in both sexes (1 mm, but clearly to be seen). Additionally, the wohle colouring and the stripes on the body are somewhat different, especially the lowest faints into a very small streak. At last, most fish are slimmer than bintan-like forms, a bit reminding at parvulus and ornaticauda. (There are broader types however, too).
The fish you describe is certainly not filamentosus but probably a bintan-like form from Sumatra. But why do you guess it’s sumatranus? This should be clearly recognizable by the structure and colours. O doubt that, not in principle, but because of your description.
If they are sumatranus, then: buy! Buy! We lost nearly all of them in our stocks! They are most interesting: with head-up display steeper than ornaticauda!