Sorry I am so long to get back to you, Wei.
I found that problem, too.
You can raise the pitch *edit [AND ROLL] from 50% to something larger in Configuration / Vehicle
OR you can change pitch limits in your TX for more collective (Spektrum can go 125%).
But, I just use System / Actuator Settings / Channel Neutral, Minimum and Maximum for leveling and getting the total collective right. I spend a lot of time here watching the swash go smoothly from bottom to middle to top and making small adjustments without running the motor. I get positive and negative pitch equal. I fold the blades together and measure between blade tips. 100 mm gets about 13 1/2 degrees of pitch with my blades.
be well,