It is not a percentage exactly.
Once we go into PoS, block rewards will then begin getting split up with 45% going to PoS Stakers, 45% going to Masternode Operators, and 10% being allocated to a community fund for a variety of different uses.
We employ the See-Saw Rewards mechanism which means that as there are more Masternodes on the network, profitability will shift slightly towards favoring stakers (For example, 50% PoS / 40% Masternodes). As Masternodes are taken off the network and more people are PoS, the rewards will shift to favor the remaining Masternode Operators instead (For example, 40% PoS/ 50% Masternode)
The way this system is designed is that it will provide fluid block reward structures that will allow for both masternode hosting as well as coin staking to continue being profitable while providing liquidity to help promote trading.