LTC3105 conversion efficiency

Hello Sir

DC1587A7A tested
The test conditions are as follows
* Vin 0.6V
* Vout 3.3V
* Load Current : 30mA(Eff 39.32%)、25mA(Eff 39.63%)、20mA(Eff 39.75%)、15mA(Eff 39.85%)、10mA(Eff 57.99%)、5mA(Eff 67.72%)
After testing, we found that the conversion efficiency is only 40%(15mA、20mA、25mA、30mA)

But the specifications on the specifications are about >50%

What could be the problem?

(When load current is 15mA, the conversion efficiency difference reaches 20%)