I suspect that it's due to the top tube angle staying relatively similar but the head tube angle decreasing for smaller sizes meaning the stem gets brought up and becomes less droopy
Yeah that's probably it.
Probably helps if the background they are shot against doesn't have horizontal lines, either :)
Might take a punt on 6.
@Howard started
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I suspect that it's due to the top tube angle staying relatively similar but the head tube angle decreasing for smaller sizes meaning the stem gets brought up and becomes less droopy