I assume by top end you refer to > 200Hz?The top end looks very spiky
I note you haven't loaded the microphone calibration file for the ECM8000. Go to our download page and get the cal file and load it into REW. You can apply it with the IR Windows popup or take another measure to include it in your measurements.I'm using a Behringer ECM8000
Yes, use smoothing on full range plots as previously mentioned.Most likely comb filtering?
Measuring high frequency response of your speakers requires closer mic location in a horizontal 0 degree position (pointed at the drivers). The standard vertical position with a 20 degree cant is a good all round technique to use at the listening position, but it will usually result in a roll off of the upper frequencies.I'm curious about the amount of high roll off, these are studio monitors, is such a roll off common?