Youre messing up the math by not converting from SP to $.
You were supposed to get $30 worth of SP, not 30 SP.
Likewise, you did not get $49 SP in your account, you got 49SP (which is worth about $30)
Thats the difference youre seeing. Your payouton the post is denominated in US Dollars, but your payout in the author reward is denominated in SP.
I get what you are saying about the "$" being confusing. I definitely should not have used that. But I still believe I came out ahead on current value of the two options.
im 91.6387% sure that the money you seem to be ahead is reverse auction proceeds.
But like i said in the other reply, its definitely a better deal if you were going to convert to SP anyway.