Along equator, the distance between the Central Indian Ridge and the Sumatra Trench, is exactly 30°. According to the analyzis here, both ridge and trench are offset by 1.5° to the west compared with the large scale roll of lower mantle. Therefore, the distance is exactly the expected value compared with the convection rolls model.
The Central Indian Ridge is posistioned exactly in the same way as the Reykjanes Ridge compared with the large scale lower mantle rolls division line. The two layers of small scale convection rolls create a down-welling division line exactly above the large scale division, so therefore the ridges tend to appear along the next small scale division line, unavoidably being an up-welling one.
The Sumatra Trench is on 97° 20.000’E, and the Central Indian Ridge on 67° 20.000’E on equator.