What constricts the data in the different charts?

I think it's because Garmin just didn't bother to add that feature.

You could try this 3rd-party Connect IQ data field which can display your % Grade and write it to the activity FIT file to be displayed on Garmin Connect. I haven't tried it, but I think it might do what you want:

apps.garmin.com/.../4bec6b1d-2eea-4f56-9467-c609b542b2c1

Maybe this video will help:

[https://www.youtube.com/watch?v=J5IXgyBMuX8]

By the way, it seems like you may have downvoted your own comment, maybe in an attempt to undo an accidental upvote. The way to undo an upvote/downvote is to press the same button again.

If you want Garmin to add this feature natively, you can submit an idea here:

[https://www.garmin.com/en-US/forms/ideas/]

Thank you Sir, I'll give that a try.

Being closer to 80 than 70 I still prefer step by step written how-to's.

That's probably also the reason I find  some of the functions in this forum less than intuitive, but it is what it is. ;)

And setting up/changing anything on my Vivoactive HR happens in Garmin Express, 

Cheers

HJ