1. Disagree. Your sense of "realism" about where soldiers would be and how the aliens would approach the base leaves much to be desired. Aliens would not walk up to an entrance. They'd be more likely to blow it open and drop down quickly. And putting soldiers "on alert" every time a UFO is within radar range would be exhausting for such a small team.
Well, since they DON'T blow holes up, it's normal to defent the *possible* points of entry. Other than that... Any military base is defended all of the time. And even if you insist that "realism" is everyone sleeping until alerted... AND that getting on alert when the threat is high and real (it's wartime, guys), make it not "withing radar range", but an UFO withing 10 minutes of flight time to the base and heading in its direction.
2. I don't think it takes 30 minutes to move four turns.
For, no. Nine, yes. But ahem... With the overblown hyperboles you just used yourself, nitpicking on whether it's 30 or 26 minutes is *really* missing the point.
3. This does not appear to be a suggested improvement. And all of our aliens are dumb as doorknob. That's the only brand of AI we have.
There was another point that you /decided/ to skip there. Underarmed. Make sure the base attack missions have good ones (above average skills, good equipment). Maximum numbers, too.
----
So what you're asking is for an entirely new map to be created in which the player soldiers sit behind defensive positions and shoot at approaching aliens. If you'd like to, go ahead and create it. I'll even help you work out how to provide a modified .ufo file that others can download to use your base defense map instead of ours. But why would I want to put in so much time and effort on completely changing base defense missions for no real improvement in the game?
I don't say a completely different map. I said, place soldier spawn points close to entrances, not Hell knows where. And well, I'd do it already if I had an idea how to operate that editor.
... But frankly, you calling military base in war time being defended being "much to be desired" in terms of realism makes me think you *live* in a chessboard world...