I also don’t believe that you could have gained 6 pounds of fat in a week by upping your intake level. That is something on the order of 25000 calories for 6 pounds of fat. You increased your intake 25% for around a week that is only about 5000 calories in a week assuming low to high by your figures. So assuming you stored everything you brought in that might be 1.5 pounds in pure fat.
I did a lot of BMR increasing in the last few months, those were successful after I was at my maintain macros for many months, not several days, and well into fat adaption. A couple other things is that before I did this I exercised daily and very intentionally to work my slow twitch muscles and I rarely fasted but I had done it EF a few times over 36 hours. I ate until I was full, I never really restricted, and I almost always ate extra fat to the point that I desired it. My satiety took many weeks to start to work and on occasion just fails, but that seems to follow my hunger not working correctly either.
Outside of the normal eating routine if you are truly trying to increase your BMR or from my viewpoint normalize it you may have to consider timing as playing into your intake. I was 18:6 as well, when I started the routine I went from about 2900 to 3900 calories two to three days a week. So I was a little higher than 25% increase, mainly because it made my measuring easier. For best results I would eat my highest protein meal first(noon), wait at least an hour and then ingest my boosting shake which was mostly fat. The timing is the key, if you try and stuff it all in when you ingest the protein it seems to delay the actual boosting effects and I would imagine you run the risk of storing the fat depending upon your IR level. I know at least hour worked ok for me, the best results were when the rest of my day was centered around fat an not protein so much at later meals. I also used SCT’s and MCT’s instead of animal fat since they act quicker and tend to be turned into ketones. Later on I switched shift I was working and had to eat much earlier in the day, so when I would eat breakfast, I would follow it with a boost shake around 10-20 minutes later, and often had a higher protein lunch, and a more fat center dinner. This did not work as well the results were not as good, I never felt as good this way. I would also tell you what you are ingesting is also important, as much as I love steak, it does very often slow weight loss/fat loss for me mainly because I tend to eat too much of it before satiety kicks in. My best results often were when I was regularly eating salmon the day before or day of my boost.
So depending upon how far along you are on your journey I think that also will make a big impact, if you are newly or not yet fat adapted it will be a little tougher to just increase and hold. If you are increasing your protein with the fat level by maintain % 's you may also not be getting desirable results. How you feel if that is more important that weight loss then I would stay the course for another week. You will have to figure out what works for you as I did.