Somewhere in the 1100-1300 calorie range actually does seem to be maintenance level for me. Charts all indicate I should be able to eat 1850-1950 calories a day, as a lightly active woman of my age and weight and maintain my current weight. Even as a "sedentary" woman, I should be able to maintain at 1660 but at that level, I definitely start creeping back up. The charts are not effective for people with factors such as long history of yo-yo dieting. That alone might not be an issue but if the diets were extreme, it can definitely drag down the metabolic rate so you just don't burn the number of calories the charts predict.

I have a friend who went to a diet/weight loss specialist for medical treatment, it was a prerequisite of getting gastric bypass (which she has now decided she is not likely to have) and they did a bunch of tests. One was able to determine how many calories she actually needs to maintain her weight. She currently is probably 100 pounds heavier than I am and she is about 2" taller than I am yet this test showed that she would have to keep at/below 1700 calories to avoid gaining weight. I took that as true proof of the whole depressed metabolism thing.

I have gotten pretty good at maintaining in the past 2 years, when I took breaks from actively losing. This time it has been much harder to return to losing, it seems that I really have to keep the intake under 1000 if I want to lose more. I still hope to push that last 5 pounds off and expect it to be hard but I do think I will be OK when I move to permanent maintenance. That still involves watching calories and some under 1000 days but I am able to maintain by checking weight daily and as soon as it goes up more than 2 pounds (less can be temporary water retention) I take a "diet day (or 2) and that brings it back down.

I am roughly 5'3", deducting for shoes, with a large frame and at 140 pounds my BMI will be just under 25, which is the top of the "recommended" range. I'm not shooting for any more than that, it is becoming more work than I want for the sake of being lighter. I am hoping that as long as I remain in the recommended range, it will keep my body (thus my heart) happy and I will have no more Afib. I want to be realistic, It may not work 100%, but I'm hoping for good results. I haven't had a noticeable event in almost 2 years.
I have no expectation of ever being able to eat like a normal human being again. Not for more than a meal/day at a time anyway.

@DotLewis You must have a different BMI chart from the one I have been looking at. Mine gives the top of the healthy range at 29. 25 is the bottom of the healthy range. Even if I aim for the 29 point I still need to lose at least 25 pounds more. It'going okay at the moment though.