I had a similar issue, which was remedied by getting a larger cuff. In retrospect it makes sense that one size does not fit all, and apparently my biceps are on the larger side.
Cuff sizes are targeted to a range of arm sizes. The range should be stated either on the cuff or in the manual. Using improper sizes over/underestimates the pressure values.
Yes, and that's so obvious in hindsight, but the monitor I was given at the doctor's office came with a size that was too small for me. It's not something one thinks about until it becomes an issues.