The SP rate isn't that bad since the changes made in the recent patch apart from the following rank ranges.

11-15
21-25
31-35
41-50

See a pattern there?

SP is fine when you're doing new leves for a higher grade or you're just starting out on a new grade but once you're settled in to the current grade the SP is terrible until you hit the next set of leves.

45-50 is only included due to the lack of grade 6.

So what needs to happen somewhere is SP for the rank ranges I mentioned not fall below what it was at 10, 20, 30, 40 until you are high enough to scan the next grade at 18, 28, 38 and 48. Since grade 6 doesn't exist we'll have to accept 48-50 will see a lower rate of SP under this system.