Hello, I was hoping someone can confirm something for me: Does it cost 4,500 or 9,000 Avios to fly one way from IAH to SGF with a connection at DFW?

Distances (from Webflyer):

• IAH to SGF - 514 miles
• IAH to DFW - 225 miles
• DFW to SGF - 364 miles
• Sum of IAH to DFW to SGF - 589 miles

Do they charge by each leg, even if the total travel qualifies as a zone 1? Thanks!