I believe part is based on appearances, with us paying £500k for every 50 appearances up to a maximum of £2m (which is 200 appearances).
The rest is based on what we win and I think it's £0.5m per PL title up to a maximum of £1.5m and a further £1.5m if we win the CL. That's all within 5 years I assume.
So for the extra £5m to kick in we would need to win 3 PL titles and the CL in the next five years,with Sterling making 200+ appearances in that time. I think I could stomach that.
In the meantime, Milner & Benteke will probably still be looking for their first Liverpool medals. But at least they'll have played in front of 90,000 Aussies.