Mast retained a bit of inhibitory properties after conversion, but is no way worth being a primary aromatase inhibitor. Although 100mg in my case is my TRT dose, which I would not require an inhibitor at all. So yeah, low doses may not result in high aromatase (not common for someone age 50 btw). But you have other issues to attend to, masteron can wreck your lipids, you also need to watch your blood pressure as that's a serious concern when cycling at 20%.
It's really no secret. No matter how you look at it, it's unhealthy to cycle at high body fat, period. And yes, 20% is too fat. We also have to remember, the number of folks responsible to their own bodies is less than 5%. So articles like this are generally to help the 95% that want instant gratification without any regard to thier health.
Blood work is always key, but won't always save you.