I understand how you put your hand/arm on the bench if you do a 1-arm row, but how do you do it when you do it with both arms?
Any rowing movement will "work", but the real secret to know if it will build muscle is this:
During your et are you feeling the back muscles doing the job and at the end of the set are the back muscles feeling pumped. If the answer is yes, then it will work. Its not that the pump is what builds muscle (it is not), it is that the muscle that gets pumped is the muscle that did the work. So at the end of the set you can know if the exercise you did hit the muscle you want to build.