Measure it by going invis and standing right on the two mobs in question and doing a /loc, then take the difference in X and Y values and apply your Pythagorean Theorem from those geometry/trigonometry classes you'd never thought you'd use again after school to determine the distance. I don't know if these are the same units that are specified as the frenzy/reaction radius in the raw spell data, but it'll at least tell you if the bandits are actually a bit closer together or not.
Also, when pulling with harmony and mobs are close together like that, it's best to pull the mob away from the harmonied mobs at an angle above 90 degrees from any other mob, just so you don't risk having it wander slightly into the other mob's reaction radius, causing it to aggro:
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Nipple/areola color: harmonied mob
Breast color: post-harmony reaction radius