I don’t trust any graph without at least its axes and captions, so here’s the source.
https://www.ons.gov.uk/economy/inflationandpriceindices/bulletins/consumerpriceinflation/april2024
While I think the message here is important, this particular plot seems to be of “Owner Occupier’s Housing Costs” and this capture conveniently crops the frame so that you don’t see the dip just before 2019.
Oh! Awesome experiment! Yes, they’re shorter because of perspective (foreshortening). With a mirror surface it’s better to think of a duplicate of the object flipped across the mirror plane, then you can apply the same tricks to draw in perspective, which may make it look shorter.
In your example here, since we’re viewing from the side the perspective is not going to factor in as much, so we land at “roughly the same size”