I was just trying to sketch that hope the edited photo makes sense, yellow line is T down to Ufh 2 port downstairs. Green is 10mm to bathroom rad. Dark blue is HW tank feed through 2 port and light blue is to rads via the other 2 port there in the airing cupboard.Can you sketch how you’ve tapped into the heating pipework that serves the flow to the manifold. Was you aware the cylinder return is always the last tee in?
I don't know where the cylinder return is as its under the floor upstairs somewhere.