I also have an enlarged LA.
My information says that 'normal' is 1.9 - 4.0, so there is indeed a big range in normal sizes, but it would seem your LA seems somewhat enlarged. Mine by comparison was recently measured at 6.11. I get breathless when exercising hard, and recently had a pacemaker inserted to improve heart rhythm. I suggest you be as kind to your heart at you can by exercising, losing weight keeping to a heart healthy diet, including less salt, and that will go a long way to preserve your heart health.
The enlarged left atrium may be the compensation for the MVP. Mild, trivial, is considered medically insignificant and usually does not progress or cause any symptoms.
The enlarged atria should be of some concern to determine the underlying cause. The size may be normal for you and the dimensions are estimates.