If you have no fucking clue how +CA damage works, just shut the fuck up, sir. By the way, it works the same way, like +spell damage works. If you wanna know more about game mechanics, i recommend, reading
this thread.
But let me prove the case for my assertions - the following numbers are taken from the Testserver and are based on 771 str and wearing the mythical Eagle's Talon (which +10% on combat arts also works as +CA dmg).
Roped Shot (Adept III):
0 CA dmg: 489 - 816
75 CA dmg: 564 - 891
125 CA dmg: 614 - 941
200 CA dmg: 689 - 1016
Searing Shot (Master II):
0 CA dmg: 577 - 962 / 577 - 962
75 CA dmg: 652 - 1037 / 577 - 962
125 CA dmg: 702 - 1087 / 577 - 962
200 CA dmg: 777 - 1162 / 577 - 962
Triple Burst (Master I):
0 CA dmg: 368 - 613 / 736 - 1227 / 1104 - 1840
75 CA dmg: 443 - 688 / 736 - 1227 / 1104 - 1840
125 CA dmg: 493 - 738 / 736 - 1227 / 1104 - 1840
200 CA dmg: 568 - 813 / 736 - 1227 / 1104 - 1840
Shower of Arrows (Master I):
0 CA dmg: 3451 - 5752
75 CA dmg: 3476 - 5777
125 CA dmg: 3492 - 5793
200 CA dmg: 3517 - 5818
Bloody Reminder (Master I):
0 CA dmg: 160 - 266 / 388 every 2.6 seconds
75 CA dmg: 235 - 341 / 388 every 2.6 seconds
125 CA dmg: 285 - 391 / 388 every 2.6 seconds
200 CA dmg: 360 - 466 / 388 every 2.6 seconds
Searing Strike (Master I):
0 CA dmg: 14 - 23
75 CA dmg: 21 - 35
125 CA dmg: 21 - 35
200 CA dmg: 21 - 35
As you can see, the full amount of your CA dmg is added to every spell (notice the different calculation for a DoTs and AEs). As you also can see the maximum of CA dmg is 50% of the min and max values.