Why have 85% boon duration on renegade?

[Venevan.9730]

This is about the permanent alacrity uptime on renegade used for raids/fractals.
The build guides I've come across all tell me that I need 85% while anything between 75% to 100% shows no differences.
Do I get the remaining percentage to reach 100% from outside sources, or am I missing something?

[Veprovina.4876]

Is it a new guide or an old one?

 

Boons cap at 30 seconds now, so if they took that into account, it's probably the optimal % boon duration so that you can apply new Alacrity while the old one is still in effect - meaning, permanent alacrity.