Think positive:)everything happens for a reason:)

About £400

Maybe 'disposable income' would be fairer... as looked for by mortgage and finance companies.

This is the limitation of arriving at the figure as 'they' have done, by basing it on benefit rules .

I may indeed have the requisite 18,600 (gross) on paper... but if my rent is 1,000 pounds a month ?

If the £14,625 figure I used is only £400 below the 'poverty line', then the statement by @graham59 that the Minimum Income requirement (£18,600) is "only just above the 'poverty line'" cannot also be true? But, then again, it is relative - as 5'6" is 'only just under' 6'0" !!!

What they do to calculate the poverty line is.
Average national earnings minus 40% is the guide to the following years poverty line

Whatever it is... I'm hovering around it every month.

Or conversely

You might earn 15K and have no rent or Mortgage and fail

Exactly.

x.ac.uk/resources/reports/the-minimum-income-requirement-for-non-eea-family-members-in-the-uk-2/

How 18600 was arrived at

it appears that figure is the level below which public funded benefits kick in...so it just makes sure no immigrant will get any public funds......which they are not allowed for the first 5 years anyway !