Pronunciation of the letter “e” in Portuguese

I was going to say the it's pronounced with an actual "E" sound when it's the first letter of the word because I noticed that pattern in the examples you gave but then I remembered words like "essência, embrião,emoçao" so I guess there really isn't a specific rule that determines that because some words will always deviate from patterns that you pick up on like I just did, but then again i'm not a Portuguese teacher or someone who knows all the rules that go into it. I guess the only standard I can think of that determines when it's always pronounced with one of those sounds is when the "E" is the first letter and it comes with a circumflex accent(ênfase),other than that it probably just comes down to personal speaking style because not all people will pronounce the words the way the majority of people do, if you take "endocrinologista" for instance it's acceptable to pronounce it both ways, and there are also the words that sound funny and wrong if you don't pronounce them the way they're supposed to be pronounced (essência with an actual "E" sound),I'm pretty sure this happens in all languages. You'll just have to expose yourself to the language so you can get an idea of how to pronounce them naturally by hearing how native speakers say them.