I know that there is a difference in the degree of openess of the mouth when one is to pronounce /e/ and /a/, such as in words like "effect" and "fact", "every time" and "agriculture". In the past, I thought they should be distinguishable and pronounced differently all the time. But I noticed that the /e/ sound in "effect" (the second letter "e") is often pronounced by me to be similar to the /a/ sound in "fact", unless I deliberately intend to controll the openess of the mouth or adjust the natural movement of the tongue. I find that, in some words, the /e/ sound may seem close to /a/ sound, if the speaker is excited, shouting or speaking in a high voice. If the speaker doesn't want to emphasize the word, or he wants to keep the talk casual, he may keep a less open mouth pronounicating the /a/ sound. I heard in a movie, the hero (a British English speaker) said "thank you" in a way that can be heard to the similar effect of saying "thenk you". So I am rather confuesd. And I feel painful to have to make an effort when I see the next sound is /e/ when I am reading aloud or speaking something? Besides, I know that American English speakers generally tend to open the mouth more exaggerated than British English speakers. And I generally adopt British way. I still want to keep it. So the mixed listening to both American English and British English may also be a real reason that causes this confusion about the distinction of /e/ and /a/. The same problem is witnessed in not a few English learners in our country. But some may not care or notice, and keep pronounciating in a way they feel comfortable and natural. I used to do that. I know in communication this is not a big problem. I also do not have this problem in listening. But if I will be a teacher, I certainly want my English to be as standard as possible. Certainly this problem does not apply to all words with /e/ sound. Some are easy to pronounce. Maybe because of the sounds beside it? Maybe just because I haven't tried hard enough? I don't really know.