Dac channel amplitude

Device: RFSoC 4x2 Kit
PYNQ Version: v3.0.1
When I set the transmitter channel amplitude to 0.7 with a frequency of 1500 MHz, the result is smaller than when I set the amplitude to 0.6 with the same frequency. What could be the reason for this?
I am using the base notebook `rfdc 02_rf_spectrum_analysis.ipynb

amplitude=0.7、frequency=1500MHz



amplitude=0.6、frequency=1500MHz


amplitude=0.5、frequency=1500MHz

When I use rfsoc_spectrum_analysis.ipynb, the issue mentioned above does not occur.