The difference is so narrow that I wouldn’t notice any difference apart from the length, the first and last e are very slightly shorter than the middle e. And of course you have the usual going-down-with-your-voice-at-the-end-of-the-word
Yes, we often call them “long” and “short” E but the short E is actually halfway to A. It’s a different vowel even though it’s written the same. The last E is the vowel we often have in unstressed syllables like gekommen, same in English upon, about. We write it as E but it’s basically the most relaxed vowel possible.
Look at this vowel chart to see and hear the differences.