This has been explained to me before, but I need more information..
For the sake of this post I am talking about the Excel strings, like the one that came with it.
I am not getting consistency out of the strings, I have three and all three give different POI. The original is brown with green strands, the new one I bought today is all brown..
That aside, I have string "A" set up perfect, I can pull it off the bow, and put it back on and everything stays the same.
String "B" (the new brown one) needs to be twisted many many times to get to the same brace height, I like the string sitting on the line closest to the trigger. When I twist it enough to make it sit right the POI is off about an inch (low@30 yrds). I am trying to have a spare string, and without being accurate I can't call it a spare.
So my questions..
Brace height, if the string is the same why the difference in POI? I assume it will stretch a bit, but which way does the string have to move between the lines on the barrel to increase the POI, or does it even matter?
Is one string going to create a faster FPS than another, even if they are the "same"?
I really need to have a firm understanding on these things, and I can't seem to find any old info on here..

If both strings are the same and you have to twist one much more than the other that would indicate that the one you have to twist more is heavier and therefore much slower. In theory a heavier string should get you a lower POI.

If I keep twisting it will I bring up the POI?

Here's what's happening, imho. You cannot change string MATL and have same poi, no matter the brace height. As far as I know, there are currently 4 strings available. Two are Flemish, two are endless loop dacron. The Excel green and brown threads on mine come close to interchanging w/ the green and black Flemish dacron. The black endless loop is called the standard, don't shoot it, so don't know about it. The last is FFF, grey and black Flemish, which is the fastest. So, to reiterate, you can switch back and forth between the Excel and Flem dacron, but believe the rest require sight adjustments. For me, going from Excel to FFF is two clicks on V-zone at 20 yds. You might want to go to Excals site under accessories and look at them, but if I recall, they only show three.

If you take 2 strings same maker and same length both same strand count. They should shoot very close to each other, half inch of each other. You said you have one b&g and one b what is the 3rd one?

I have 2 excal strings fff they 're now both broke in and they're within half inch of each other at 25 yds. Black and gray. I have 2 others excal excel all brown endless loop strings, don't have them broke in. They be slower than molasses!

Both of these string are the same material, I pulled open both boxes myself and they both said "Excel".
Thats why I was hoping the brace height would make a difference, my one on the bow right now is not twisted, at all. The new one I bought today required several twists to achieve the same brace height, the POI difference is not big, but big enough so I know it can't be used reliably as a spare.
Should it be twisted a bit? I can readjust for a twist, but what difference does a twist make? Why is the point of a brace height?

*EDIT* By "spare", I mean a second string that can be replaced in the field without readjusting.

Brace height=most efficient return of energy stored in limbs.

OK my excel strings are b and gn. one is about 3/16" in length longer and it fits without any twisting. So the shorter one won't need any twists either.

Fair enough, I get that.

How does one achieve proper brace height? Let me guess, back to Bass pro for another tool..Knowing the speed of my arrows sure would help things..

I seem to be having a bit of a mind block on the combination of variables from the string material to the amount of said material to where that material sits on the brace..