Arc Flash Boundary above 600V

I find this a little confusing and could use some guidance. Lets say we are using the analysis method. We need to calculate the Arc Flash Boundary. We have the choice of the Ralph Lee equation or the IEEE 1584 equations presented in the Annex D.

Now, my opinion is that since the Ralph Lee formula is part of the original code, it must take preference over anything in the Annex. The problem is that code stipulates that the Ralph Lee formula is only good up to 600V.

The IEEE equations in Annex D, I assume by the introduction, are good up to 15KV. But there is a variable, that changes value, whether it is under 1KV or over 1KV.

So would this mean we use the Ralph Lee formula up to 600V, and then switch to the IEEE formula to 1KV, and change again above 1KV.

I know you could use the IEEE formula at any value below 1KV but it seems contrary to substiture an Annex formula in lieu of the code supplied formula.

Am I over complicating this or did I miss some fundamental point?

In general, most people use the IEEE formulas up to 15kV, and then revert to either the Ralph Lee equations, or another model like the Duke Energy calculator, or ArcPro.

As to you complicating the matter, I don't think so. See http://www.arcflashforum.com/showthread.php?t=50