I personally think 10 frags is already pretty good, altho I did get RS like 3 times. but there's an organisation design formula that says something like the ammount of work will suit the ammount of time, meaning that if you make available 4 hours or 8 hours, for some sort of job, you will (if your time planning is above the minimum time needed to complete the job) do the same ammount of work needed to compleet the job, only if you have a schedual of 4 hours you will ofcourse work harder and if you have 8 hours you'll work more relaxed, detail things out, do some thorough research etc. in reflection to this tibia server you could say that the ammount of frags needed for red skull is either 10 or 15, you will still get red skull in most cases if you set out to get red skull (or as many frags as possible, help your friends as best as possible etc etc) simply because there is excess supply of unjustified frags.
more ins and outs about organisational design or behavioural economics can be retrieved through an ingame message.
thank you for your time,
Professor FETBOJJ