Maintenance for the week of April 20:
• [COMPLETE] NA megaservers for patch maintenance – April 20, 3:00AM EDT (7:00 UTC) - 12:00PM EDT (16:00 UTC)
• [COMPLETE] EU megaservers for patch maintenance – April 20, 7:00 UTC (3:00AM EDT) - 17:00 UTC (12:00PM EDT)
It's 6% increased block mitigation, block mitigation starts at 50%, so you are getting a 6% increase to that 50%: 1.06x50=53. This is why you will need 80% increased block mitigation to reach the cap of 90% damage blocked.