When you see something expressed as a %, the % is always of the cumulative total. Example, 1:1:10% would equal 10 (1) ounces+10 (1)ounces +2 (10%) ounces. If you see someone refer to 5% for example that would be the amount added to the total of whatever the mix ratio of the product they are using is. UV Clear mixes 1:1 so if someone said add 5% retarder it would mean 5% of the cumulative total. Say you mixed 40 ounces total of UV clear and activator, you would then add 5% of the total of 40 ounces, which in this case would be 2 ounces.
Hope my explanation is somewhat understandable.