This is very common for parts like this. If you look in thingiverse for pictures of this calibration pyramid, you'll see hundreds with the same problem. And yes, you are correct, it's just lack of cooling at the very top. Here's a few suggestions for ways we have been able to improve printing of extremely small layers like that:
- Lower your extruder temperature by 10-15 degrees - Some of the best calibration pyramids I have ever seen with PLA were printed at 175 or 170 degrees. A lower temperature lets the layers cool faster and helps the plastic solidify quicker. In Creator you could even slice the part, preview it by-layer, and find out the layer number where the part really starts to narrow. Then go into the Temperature tab of your FFF settings and start lowering the temperature near that layer using additional setpoints.
- Improve your cooling fan - Very small parts like this need as much cooling as you can give them! This is one of the big reasons you see people attaching ducts to their cooling fans to help concentrate the cooling fan air near the extruder tip. You might try adding a similar duct to your M2 fan for parts like this, or even look at installing a second fan. Both would help.
- Try printing the same part in ABS instead of PLA - It wasn't clear from your post, but if you are printing with PLA, you might want to try printing the same part with ABS. ABS is typically less stringy and can solidify quicker because of its higher glass transition temperature. It's the same reason why bridging is sometimes much easier with ABS instead of PLA.
- Print 2 at once - Obviously printing multiple parts at once means that the hot extruder will have to move away from the part momentarily while it prints the other part. We commonly solve cooling issues by just printing 2 copies of the same part simultaneously.
Hope that helps!