Thank you for responding.
I don’t understand why Custom Dim. would be more interesting than Custom Var.
As for my case I would like to add the ratio of visible content vs content height to the pageview hit.
I added this information as a Custom Dim. but like this, the most important data is the ratio and secondary data is the page. I want to see a mean of that ratio for each page.
So I think that Custom Var. would be more relevant.
But in the Tag Manager, I cannot add Custom Var in the Matomo Variable nor in the Matomo Tag.
May be I just need to learn how to do this…