I wouldn’t trust a self-directed test of maximum heart rate. It would be very, very difficult to get an accurate result. It’s hard enough to go to a true maximum in a lab.
But the good news is that you don’t need to know. If you’re testing your actual thresholds, then maximum heart rate is irrelevant. Here’s a rough hierarchy for establishing training zones. Whatever level you are on in the hierarchy, you can ignore everything below:
1. A gas exchange test
2. A lactate test
3. DIY anaerobic and aerobic threshold tests
5. Generic formulas (of which MAF is one…)
You’re comparing numbers 3 and 5 which won’t help you. Now that you’ve tested one of your thresholds, you can ignore the generic formula. It doesn’t tell you anything other than it’s a coincidence.