HRM question

I just got a HRM and tried it out today. I plugged in the numbers and my max HR is supposed to be 178 and my "fat burn" HR is 125.

I've been doing Insanity for about a month now and going at the same pace, the HRM showed that when I'm fully engaged in the routine I'm about 145-150 BPM..way above the desired 125 BPM to burn fat..which I was surprised.

The thing is if I slow down to 125 BPM, I would be doing the workout routine REAAAALY slow, almost enjoyable..hehe

So, my question is:

1. Do I slow down my routine to accomodate the ideal 125 BPM to burn fat? (which actually seemed awkward)

2. Do I just maintain the HR I've been currently doing..which is higher?

Has anyone else run into this?..basically I was surprised my heart rate was so high for the routine I was doing. I can manage it, but seemed like my heart rate should be lower.. Even at the higher heart rate it wasn't a problem for me..but is something wrong with the HRM then?