Your math was correct, in that it caclulated the change in the percentage of Grazes that would convert to hits. I just took it the next step, by expressing it as a percentage of all attack rolls, not just the ones that resolved as a Graze on the first pass. [EDIT: And I did it wrong-- math now fixed below!] And I was only talking about the marginal increase that you get from Confident Aim, not the total of the PER inspiration and Confident Aim.
To illustrate, assume that you're attacking an enemy with a weapon you're proficient with, and your total ACC is perfectly equal to their Deflection.
With no buffs: A straight d100 roll against the game's thresholds. 24% chance to Miss, a 25% chance to Graze, a 50% chance to Hit, and a 1% chance to Crit.
With just Confident Aim: As above, but add 30% Graze-to-Hit after the initial result. 24% Miss, 17.5% Graze, 57.5% Hit, 1% Crit.
With just Disciplined Barrage: the +5 PER translates directly to ACC, which shrinks the Miss window and adds to Crit. Your first pass results in a 19% Miss, 25% Graze, 50% Hit, 6% Crit. Then you apply the 50% Graze-to-Hit conversion for 19% Miss, 12.5% Graze, 62.5% Hit, 6% Crit.
With both Confident Aim and Disciplined Barrage: As above, but apply both G2H conversions sequentially. 19% Miss, 8.75% Graze, 66.25% Hit, 6% Crit.
Lastly, remember that this is a best-case scenario. If you're fighting an overpowered enemy or if you've buffed your ACC and debuffed your enemy signficantly, you might have a smaller initial Graze window, which would reduce the number of times that the conversion is relevant.