Tax Credits disregard and Gift Aid

Hi,

Can someone clarify what is meant by the "Income rise disregard" and "Income fall disregard"?
I'm only really interested in the final award, rather than payments made through the year.

Say in 2016/17 you had an income of £30,000.
1. If you have an income of £32,500 in 2017/18, does the income rise disregard mean you would receive the same tax credits as if you had an income of £30,000?
2. If you have an income of £27,500 in 2017/18, does the income fall disregard mean you would receive the same tax credits as if you had an income of £30,000?
3. And so an income of £32,500 gives you the same tax credits as an income of £27,500?

4. If you have an income of £32,501 in 2017/18, does the income rise disregard mean you would receive 41p less tax credits than if you had an income of £30,000?
5. If you have an income of £27,499 in 2017/18, does the income fall disregard mean you would receive 41p more tax credits than if you had an income of £30,000?
6. And so an income of £32,501 gives you 82p less tax credits than an income of £27,499?

Thanks,
Jim