Ful-Base actually calls for 1 oz. activator for every 24 oz. RTS material (4.2%) but that would be of their own activator of unknown strength. I tend to go a little over on activator when using Nason (5%) because it makes me feel better about using cheap-ass paint, but adding 1:32 (3.1%) like you are doing is probably fine. A lot depends on which activator, for example, Euro activator is much stronger than Universal activator, since the latter already has the right amount of reduction built in. If I was using Universal activator, I would tend to go a bit on the high side.