Well - 1/730 should be correct (the reward formula is (CoinDays x 0.5 / 365))(Or just plain and simple (CoinDays / 730). Most adresses I checked got between 50 to 70 % of that - not because of a different formula, but because there are to many inputs waiting for reward, and so the network weight is still building up. (Splitting of inputs goes still on, although there are already far to many staking inputs) IMHO, an average staking time of 3 to 9 days per input would likely be optimal, so the network would need about 1200 - to 1600 staking inputs - there are certainly many more...

But if you get 1/600 per day, you must be a special case - so we would have to look at the relevant details - for that we would need to no what adress your refering to...