ESA top up and child tax credit, anyone?

Hello there to all. New member ahoy!
Ok, good people, straight down to it, husband was one of those who migrated to ESA from IB back in the day. So he claims contributions based ESA and was placed in support group.

He was claiming for me at the time he migrated and still does. The claim has always been contributions based but the top up is income related as I don't work and only claim CB/ CTC/ HB and council tax help.
As you know, this amount would never increase post migration (£154.60 a week paid fortnightly, £109ish being the contributions bit, the rest a top up) but we were caught up in the underpaid group and as a result have received back pay this week.  All is well and understood on that front. But a thought occurred to me this afternoon.....

So, naturally, being in receipt of child tax credit I informed HMRC as our income has increased by 20-odd quid a week (I'll tell the council when I've sorted HMRC.)

Now here's the bit I need help with, if anyone has the answer I'd be so grateful.

For all these years I've been putting the full amount of benefit into the "taxable social security income" box (around £8000 each year) on the tax credits form.

Have I been making a huge mistake all these years? Should I have left off the top up (which was around £30 a week but has now increased to around £50) and simply put the contributions based payment *in the box"? I should add the CTC is £64.34pw currently.

I've already rung HMRC this week once, and my shredded nerves can't take another phone call (fair enough, autism!!!) so it's over to you......be gentle with me, it's been a bit of a week!!!!