Hmmm.. this is strange, i stake more then 50 millions ECA but i get aprox 65-75k every 2 days which is not 50%/yr.
Well, the System seems to have a bias to slow rewarding down... When a wallet has accumulated sufficient staking weight to get the next block, the preference seems to go to the input with the lowest reward, as long as this input can still be split in 2 outputs..(that is: has coin age below somwhere between >11 and <12 days).
Small rewards keep the weight of the staking wallet high, so allowing for higher staking frequenzy - and smaller inputs require more blocks..
But probably this has gone a bit to far..
IF - and only IF - the observed possibility to auto-merge inputs upon reward only considers maturity (and not only applies to very small inputs), this should iron out eventually... But probably somwhere around an average maturity of 25 days..