The Maths Are Hard

Okay, not really.  I'm adequate at math, despite the B- I received from my college math professor (I'm looking at you, grade-curve spoiling math majors).  But when it comes to this kind of stuff, which is really straightforward math, I get a little intimidated.  It's wood, but for some reason my brain says, "Oh, I bet that bathroom really could use a good scrubbing."

So here we have me as I went out to measure the porch:

Handy measuring tape and pad of paper with porch roughed in...

This is what I came up with:
For the side nearest the driveway, the bottom where the wall will sit measures 83".  Up 36" from the base of the columns in that opening measures 82 1/2".  The columns narrow as they go up.  See the problem?  That second measurement should be bigger, not smaller.

Not to be daunted by mere measuring issues, I moved on to the next opening, between the two front columns, which also taper ever so slightly towards the top.  The bottom opening measures 84".  Up 36" from the base, the opening measures 83 1/2".  Again... should be a bigger number, not a smaller one.  Right?

But whatever, it is math, right?  I moved on to the next opening - where the steps are.  bottom measurement is 50".  I didn't bother with the upper measurement for railings 'cause there's going to be a door there.  A 30" door.  Which means there will be a tidy 10" on either side of the door.  Sort of.  Because once again, the column narrows as it goes up, so that 10" on the column side will obviously be a bit bigger as it goes up.

I think that says it all.