Based on data usage patterns, AppLovin estimates that the ratio of iPhone 6 to iPhone 6 Plus devices in circulation in China is now 60:40.

In the US the ratio was 75:25 as of 7 January. That ratio is up from 65:35 in China and 80:20 in the US when AppLovin first estimated the split in November.

The 6 Plus is growing in popularity in China, AppLovin said, but it’s starting to plateau (see chart below, click to enlarge).

The market share of the 6 Plus is important because Morgan Stanley estimates that the profit margin of the 5.5-inch device is as much as 61 per cent higher than the iPhone 6’s margin. In addition, China reportedly was the largest iPhone market in Q4, outstripping shipments in the US for the first time.

These two factors could significantly impact Apple’s earnings. The company reports its Q1 results next week.

AppLovin said the increase in the ratios towards the Plus are significant since the new ratios aren’t just based on new sales, but on all iPhone 6 units in the market. It said that because the original devices sold in the first couple of months at a 65:35 or 80:20 (US) pace are still active, the new devices added have to dilute the original ratios, so the ratio of new iPhone 6 models now being sold in China is likely closer to 55:45 (6:6 Plus).

In Hong Kong one mobile operator told Mobile World Live that the sales ratio between the two models is close to 50:50, but now leaning towards the Plus.

AppLovin tracks usage to estimate the device ratio and doesn’t measure unique devices.