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Yes, the more staked coins you have , the bigger the rewards. But split them in multiples of 800 or 900 or 1000 (upto 10 per wallet) for maximum rewards. As detailed in the earlier reply this was a recent serendipity for me as well. But found a post in pivx forum detailing the same. Try it out and let me know please.
Cheers.

To date I have not seen anything that helps me to understand how to understand this "intra wallet transfer", which is "very cheap". I'm thinking that this term relates to moving stuff around inside the wallet or is it that it's cheap via the fact that you are just sending the stuff out and then back into the same PIVX wallet that gives it the term "Intra wallet transfer"?, which makes it cheaper than sending to the outside world?