In between sizes

Mine is the same. Medium is too small and large is a little too big when it is the tightest. I am also losing weight so it is only going to get looser.
 
I should have done this sooner. Measuring from the mid-point of the HR sensor to the back of the display, a Large ranges from 42 - 51mm. Keep in mind that doesn't leave any "squish" factor. Playing around at different points on my arm, I think 45 is probably about the minimum size for a Large band.