Metabolic rate calculations with the equations do not take into account the degree of muscularity of the person in question, therefore are only marginally accurate. One formula strictly uses activity level and body weight, the other uses body weight and age.
Chances are that the equations are grossly underestimating your resting metabolic rate, based on your body comp.
Funny you should bring up this topic--I just bought a little gadget to use with my clients called a Body Gem. It directly measures resting metabolic rate by measuring the volume of oxygen you inspire vs the amount you expire. The volume of oxygen you consume is the best way to accurately determine your resting metabolic rate.
If you are maintaining your weight on 300 more calories per day that the RMR equations tell you that you should be consuming, your RMR is higher than their estimates indicate. If you want to gain weight, try adding the 200 calories per day it suggests on top of your CURRENT daily intake rather than at the intake the equation says you should be.
Maribeth