It's normal, I have similar results with LRP Pulsar charger as well, what you can make a higer number is discharge them with a balance discharger, leave for a while (few horus) then you may make close to 3300...
老人家 suggested to se Peak Sensitivity to 8mV-15mV
I tried with 9mV, and I could charge up to 31xx on my GP3300. Will try higher mV next time, and let you know.