I'm not sure of the exact waza you were trying but I think that relaxing is important, yes. But... Maybe the problem could be your form. Morote dori waza is very important to stay away from the direct resistance, right? You wont be able to lift your arm(although),, Eventually this resistence thing wont matter much anyways. My guess is your still trying to do the waza from your arms. It takes a long time to learn how to use your whole body and maked all the timing correct with it. Tell your ukes to lay off and let you get the motions right. If this is still your first or second year, they should be giving you minimul resistence.