This applies to all membranophones.

When you tune a drum, and notice that one point of the drum is out of tune, you don't necessarily need to adjust that point on the drum.

Using your example, if one spot sounds low compared to other points on the drum, try increasing the tension (tighten) the lug directly across from the problem spot.

The points directly across and on either side of the "problem" spot are where you'll need to adjust to fix the "problem" spot. I know it seems that you need to adjust right where you are hearing the problem, but that's not how membranes react and vibrate.

Something you can do to help you with this is to tap where the "problem" is, then check directly across and on either side. Compare all these points then adjust accordingly.

Make changes slowly, taking where the problem spot is ... and hear the change take place as you increase/decrease tension.

Cant top what these guys have said, but
tuning in diagonals is the best method I find to get a balanced tone.
However, with my hand percussion sometimes its nice for it to have different
sounding sections on the head - especially if you only have 1 drum.

the Remo Mondo-style heads are pre-tensioned to begin with - if there were any inconsistencies "pre-tuned" into the head, it makes it more challenging to tune those out of these instruments. Not impossible, just more challenging.

Personally, I have yet to meet one of these mondo-headed drums that were absolutely uniform and perfect in it's "pre-tuned" state, prior to adding any additional tension or fiddling with individual tension rods. (I haven't met them all, I'm sure there's some more uniformly tuned mondo-heads out there  )