Child Maintenance - 25% Rule

Hello...

Is anyone else really struggling with this rule that if your income doesn't drop by over 25% then your child maintenance payments remain the same as they were when originally calculated.

I think that's absolutely draconian. How out of touch are the people that have put this in place? Who out there (that's working class) could absorb a 20-25% reduction in income and still get by ok?
It's bad enough that it's worked out on your pre-tax income, so not only are you paying that amount, you're also paying the tax on it even though you (in effect) never have it.

In my case, I do self-employed work on top of my full time job to try and provide for my current family, while what I make helps us, it does not account for 25% of my total income. On the year that the original calculation was made I had a particularly busy year, but the years since have been reducing continuously to the point my recent return was below half the amount of the calculation year. But while the online calculation says I should be paying less CM, they won't change it because of this 25% thing. All my SE work and time spent is now doing me no good, in fact if I cannot maintain it I'll effectively lose my home or at the very least struggle to make ends meet... with a child on the way also I'm despairing at the situation this is causing.

Does anyone else find themselves in a similar situation over this? I'm not looking to avoid paying maintenance, I've always paid it and will continue to but at this rate it's simply unsustainable unless I somehow have an upturn in my financial situation (bet the 25% change rule won't be taken into account then)