Lime API TX gain vs freq

I am new to LimeSDR and for introduction I want to use it as general purpose RF generator. Using LimeAPI calls from LimeSuite works well. To have better interactive control and enable scripting I build some command line wrapper around API:

(a basic example to integrate into python script using popen is here:

First tests were restricted to cw mode, to get stable setup 2 main findings:

  • LMS_SetNormalizedGain more reliable then LMS_SetGainDB
  • after changing frequency/gain parameter signal is often unstable, need to send LMS_SetSampleRate again

Below is result for 5 gain steps and frequency range 400 - 2500MHz in 10MHz steps (power measured with Spectrum Analyzer FSP90) :

I always use LMS_PATH_AUTO in set Antenna.
My question: are these curves as expected? Anything possible to flatten the curves at higher f?

Thanks, Martin