I read your question and I understand your concern. Ramipril and Perindopril (Coversyl) belong to the same class (ACE inhibitors), same mechanism of action and should have similar efficacy. So technically speaking no reason to expect much of a difference between them. But sometimes clinicians base their decisions also on personal experience, maybe he had very good results with Coversyl in other patients before, or has had good experience and a high regard for the quality of the drugs of the company which manufactures Coversyl. If your blood pressure is not well controlled anymore with ACE inhibitors alone (10 mg of Ramipril or 8 of Perindopril is not a small dose), an additional drug of a different class could be added like a beta-blocker, diuretic or calcium blocker. I hope to have been of help.