In the league and the cup the ideal partitioning depends on the fan base and fan satisfaction of your opponent. If that's better than yours, use 85%-15%. On the other hand, if you have a significantly higher fan base with a high fan satisfaction, use 95%-5%. Of course you can select something in between if the difference is small.
For friendly (cup) games it's best to use 85%-15%, since with a decent capacity you will never be able to fill your 85% anyway.
If the fan base and fan satisfaction of your opponent is a lot higher or a lot lower than yours it will influence the calculated result considerably.