Plus 1 corruption on Archmage doesn't apply the plus 1

Hi the Plus one i have on my archmage corruption doesn't apply even tho the tool tip goes from 8 percent to 9 percent it doesn't give me the 1 percent effect and tested between a level 19 gem with plus 1 corruption and plus 1 support and had less dps then with a level 20 gem not corrupted, with a plus 1 from support skill and my dps would go up with that