Be they the same species there are two variants to Purpleheart, Lowland and Highland. It is possible to have a good guess as the Highland is more dense, the grain is a lot tighter. If you finish the Lowland by sanding and putting a polish directly on it it doesnt work as well as sealing it first with either cellulose sanding sealer or my preferred sealer, EEE cream. Then put the friction on top. If its still not working then sand to 600. Highland is easier to get a finish on and is more dense in colour.