UC - Journal Question

Just when I think I'm starting to get a grip of this UC stuff yet another demand for info is made that I don't understand. It seems to me there are extra layers of torment involved when one is self-employed!

Today (Monday), I was first asked to confirm my self-employed income and expenses for my first UC payment, this is £0 for both because I've stopped work due to illness. I was also found 'not gainfully self-employed' on my initial visit with my work coach.

After answering the questions I then received a series of questions under the heading: 'Confirm previous earnings from work completed'. I was asked whether:

In the 12 months before I claimed Universal Credit did I have:-

- Gaps in my employment?
- Lived with a partner?
- Earned less than £542 a month?

My answers were No, No and Yes.

I read on the Gov website that the 'Earnings Threshold' is £793 per month for a single person. Can someone explain to me please why they have asked me if I earned less than £542 per month rather than £793 per month? I was getting Working Tax Credit of £163 per month but adding that figure to £542 per month equates to £705 per month not £793.

If in any of the 12 months I earned more than £542 but when added to the other months the total earnings for the year did not breach the overall earnings threshold, would my UC payments be lower in some months and higher in other months? Are they trying to apply the Minimum Income Floor to me even though I'm not gainfully self-employed?

I feel I should understand this UC stuff by now with all the research I've done but I find myself getting ever more confused by it!