that one big jump around dec/jan18 was actually an accident, I accidentally powered up my entire steem balance instead of the portion I intended to (I had just received a large bonus from Curie for one of my recommended curators performing exceptionally well over first 6 weeks). While I was earning a decent amount of Steem from Curie I was doing a mix of powering up and taking some off platform to invest in other coins (plus ~25% I donated through contest sponsorships and what not). For the most part there was an inverse relationship between earnings from Curie and earnings from my posting; the more time I spent at curie, the less time I spent at posting. So that helped keep my chart steady I think, no matter how I was spending my time on steem
EDIT - and now that I am spending my time more at @c-squared, that time doesn't actually result in any earnings for me so I have flattened off a bit lately with less posting