Nice, clear explanation.
I think for simple folk like me who don't like to look at the markets, the following simple suggestion works: when you post, pick the 50-50 option, and then do literally that, i.e. leave half the money in SP, and withdraw the other half when it reaches a certain threshold (e.g. 100 steem dollars). Unless there's some very noticeable change in steem value, don't even bother checking the markets. I mean, that's what you do in real life: you don't check the markets every time you buy clothes or a cappuccino.