Figure 7. The mass growth of two planetesimals in the outer disc (Red) and inner disc (Green). Initially, both planetesimals have ½ of the Lunar mass; the one in the outer disc accretes cm-size pebbles, whereas the one in the inner disc accretes mm-size pebbles, with ½ of the total mass flux (due to the sublimation of ice at the snowline). Thus, the planetesimal in the outer disc grows to 20 Earth masses in the time when the planetesimal in the inner disc reaches only one mass of Mars.

Source: Morbidelli, Lambrechts, Jacobson, and Bitsch (2015).