OK, well the buffering is the total alkalinity. When you add baking soda, it goes up. When you add soda ash, it also goes up.
But the problem with T/A is that as the pH rises, so does the measured T/A.
1) Bicarb raise T/A but may raise pH some.
2) Sodium Carb raises pH and T/A, part to do increased T/A, part due to the pH effect on T/A
3) Borax raises pH but the increase in MEASURED T/A is function of the pH rising.

The way I look at it, from a pure pool maint POV, Borax + Baking Soda does the same job as Washing Soda (pH Up!)

Your T/A is now plenty high at 100ppm. You should only raise pH by Borax or aeration (which doesn't raise T/A). However, with a vinyl pool, if you don't add calcium (which you don't need) your T/A won't give you trouble. Right now, mine is "low" at 40 but since my pH is fairly stable, I don't care (vinyl as well).

FC and TC being the same is good--it means CC is 0 and that's what you want.

But, the last key is the stabilizer/CYA level. This alters what the "ideal" FC level is. If your CYA level is between 0 and 30, then an FC of 3 is fine. But if your CYA level is between 30 and 50, you are pushing your luck with your FC at 3. If it's over 50, you are taking a risk with FC at 3. So, your CYA level is the third really important factor:
1) Chlorine level
2) pH
3) CYA level.

Carl