So on the face of it you fall within the definition of 'normal' and yes a lot of caffeine will cause this problem.
I wonder if you can bypass your AME and discuss it with your regulator.....
An electophysiologist will look for abnormal electrical pathways in the heart that we dont think you have!!! It is possible he or she will look at your results and say 'rubbish'. At the other end of the spectrum they pass wires from a blood vessel in your groin into the heart to measure the passage of electricity in different parts of the heart and identify the problem.
Now this is very common and if needed no big issue - takes an hour or so and home you go. However, there is a small risk of damage to the blood vessel and issues within the heart. If they do recommend this - and they wouldnt do it the same day - I really think you need another AME or to get confirmation of need from your regulator
No I am not an AME, just a doctor and pilot.