it was pretty wind this whole weekend, 18-20mph according to the internet. As a fairly avid road bike rider who pays attention to wind conditions, it felt all for real 20mph. So relative to my shooting direction being 12 o'clock, I would say the wind was blowing in an 11 o'clock direction. My best guess is that it had long gusts up to 20mph but was a fairly consistent 8-10mph when it wasn't full speed.

What does a large tail wind component like that do to your rifle shooting?
In case it matter, i was shooting 168 and 175gr 308's at 200 and 400 yards.

Head and tail winds are the worst conditions to shoot in for long range shooting. B/c it is never an exact head or tail wind. The wind will move you around more with a slight change in wind direction from the 1 or 11 o'clock position. You will get groups what will string right and left. If you are shooting at 100 yards, it's not that bad. But further out, it amplifies the right and left.

Agreed w/ Chad...also something to think about...there is always vertical movement with wind from any direction (that's a head scratcher for most) but even it just a little...it's there.

Spend some time on the 1000 yard line at tacpro. The range faces straight north, and you can see first hand what chad is talking about.

The key is to watch how the mirage is acting.

Yes. I'll take a full value 3 o'clock or 9 o'clock direction before I'll take a head or tail wind!

Some questions:

Even at as little as 200yds, is it reasonable to see a POI shift vertically?
More generic wind shooting conditions, r you suppose to try and shoot between gusts if your shooting in the wind anyways?
Is there something wrong with the way I am sitting or holding the rifle when I'm on a bench (a solid concrete shooting table) and a strong gust of wind moves me enough to see it in my scope? This was not so much a problem when I shot prone.

You will see no to minimal POI shift at 200 yards vertically. If you get 10+ mph winds, you can start to see some POI shift at 200 yards maybe side to side.

As Chad said, its almost never straight ahead 12 o'clock which will cause the mirage to boil, and its almost never 6 o'clock which will cause the mirage to boil. Most likely its 11-1 o'clock or 5-7 o'clock. That's when you really have to pay attention to which way the mirage is leaning and hold acordingly. I've had several students come out and we had a tail wind down the range. I tell them before we ever start shooting that "there will be times that I tell you to hold X tenths of a mil left and seconds later tell you to hold X tenths of a mil right." Called fishtailing.

I've not observed vertical changes with a .308 Win, and a head or tail wind, until 600 yards and beyond. And then it will only be a tenth Mil up or down in most cases. Get to 800 yards, and beyond, and it can magnify.

Here's a good example of your question. First 4 hits (top set) were with a tail wind the lower 4 were with a head wind. Now granted this was at 1000 but still a good example.