Patti,
Thanks for your question.
If a BP cuff is too small for a given individual, the readings tend to be higher because the cuff actually stretches when inflated. A larger cuff will give a more accurate reading, because the cuff is inflated without strectching the ballon inside. It's OK to use a large cuff on a normal sized arm, but not OK to use normal cuff on a large (or very muscular) arm.
Bring this to his doctor's attention on his next visit for his opinion.
Best wishes.
Martin Cane, M.D.