Just a few comments as I read through your info.

HRM for HIIT is going to be inflated. The formula for getting calorie burn from HR is based on steady-state same HR for 2-4 min aerobic exercise.
HIIT if done correctly is opposite of steady-state and at least half anaerobic.
So inflated calorie burns, and that's if your HRM could even be trusted for you.

Still good workout, for those that don't want to lift and only do cardio, it's as close to getting the body to respond like it was lifting, kinda.

Just curious, what is the gym calling HIIT now a days, what is the actual workout and timings of hard and easy efforts?

Since your prior diet method had you ending up skinny fat, taking a deficit at a healthy weight is the WRONG thing to do.

But also starting with the wrong estimates won't help either.
Use the spreadsheet on my profile page to get decent estimate of bodyfat %, and better Activity calculator for that workout, if you still do it. Stay on Simple Setup tab, and Progress tab. Your workout is High cardio. And 35-45 min is 40 min x 5 if you keep doing it.

Your BMR is likely lower since higher than average BF%. Meaning TDEE is lower too for some stuff. Spreadsheet handles that automatically.

You should take NO deficit, or indeed enter that 2 lb goal loss, which will be very minor deficit.

You will get the best improvements from your workout eating at maintenance (actually in surplus, but that's for later).
As those improvements go on, you'll be burning off the fat, while weight stays about the same. Some improvements cause weight gain.
For instance HIIT is total carb burn, hence the body responds by storing more carbs, which stores with water, which increases weight. And muscle size since that's where it's stored.
But fat will still be burned at max to support those improvements and the hard effort you can put in to the workout.

But I'd suggest you look in to doing some strength training. But that's why I asked what the program actually is. I've been finding many gym classes are jumping on the HIIT fad, and just name their circuit training class as HIIT. But circuit training is strength training, so that's good.

If you really don't want to go back to lifting, that's fine. But that's the workout that will call on the body to make the most changes and burn the most fat. Cardio, even HIIT if it really is, will be slower, well, again depending on what it is.

As to time at reset, depends on how much damage that 6 months did prior, and genetics, and other stresses against the body.

As you are coming up, you'll get an idea.
If each week turns in to maintenance with no loss or gain as you near TDEE - then likely not doing good. Staying at TDEE and in fact testing 250 more would be good idea.
If few last weeks prior to estimated TDEE cause some weight loss - then good because body speeded up enough to give you a deficit. Just couple weeks hopefully at TDEE is good.

In the following study, it took 3 months eating at lab measured maintenance, not potential, real maintenance, for RMR to increase half of what it was suppressed by. So was by 500, increased to only suppressed by 250 about.

http://www.myfitnesspal.com/blog/heybales/view/reduced-metabolism-tdee-beyond-expected-from-weight-loss-616251

So you are hoping that by going up a tad over probably real maintenance, you are getting that speed up faster. Hopefully.

Only that much for Insanity?
Or it is only 30 min, that seems low for the "intervals upside down" method of high-end aerobic/anaerobic range mainly.

10 lbs to go should be 10% actually.
Unless you want another fight on your hands you'll lose, and not weight.

You might use 15% until you hit 10 lbs left, so biggest deficit while metabolism is humming along.
Then switch to 10% and eat more and hopefully don't scare body in to slowing down again.

It appears it was more than willing to speed up metabolism fast - but that probably means it is more than willing to slow down fast too. Why risk it and drag it out even longer?

And TDEE may change now too with new workout schedule?

Totally forgot to include question in there - how are you determining the calorie burn during the exercise?

And since I think I know the answer - what make and model?

You have access to treadmill?

So the cheaper Polars are missing a key stat to improve calculations of calories burned related to HR - VO2max.

It calculates it based on your BMI (height & weight) and where in healthy range is that (gender & age) to decide if it is higher or lower.

That assumption has some problems, namely you can get cardio fit faster than you can lose weight.

So a low HR during a workout if you are fit means you didn't need the heart pumping as hard to supply needed oxygen, but you burned just as much as if unfit and higher HR.
But the HRM doesn't know that, it sees lower HR, assumed not great VO2max (fitness level), and calculated lower calorie burn.

That could be one reason.

Other more likely, since you do reach higher on your runs, just tired on the P90X and not getting the HR as high.
HRM on that type of workout should actually be inflating the calorie burn, because it's totally the wrong kind of workout for it.
But if you are attempting it tired, you may be making it more steady-state aerobic than what it normally is, which is totally varied anaerobic workout.

Eating more will help recovery, and may aid in being stronger for those workouts.
You ever see his calorie goals for his workouts. That may shock you too.