hi raincoin
i realized this recently by pure chance. Previously when i staked pivx (in April 2017), I had 2500+ coins in one address and was rewarded 6.6 pivx for every generated block.
This time around when I re-started staking (in May 2017), I had transferred pivx from exchanges using 4 different receiving addresses. Unknowingly I ended up having 1500+, 900+, 800+ and 600+ in each address and staked. To my surprise I received 4.2, 4.3 and 4.4 pivx for the addresses having 800+ coins for the same duration of staking.
Following this I went back to pivx.org and there I found a post detailing the same thing. The author there has advised splitting it into 1000 coins per address.
This is from my personal experience.
Please try it out and let me know
Cheers.