In low mode the input signal is mixed with the Local Oscillator from the SI4432 to produce the IF.? This IF is filtered in the SAW filters (B3550 or whatever you used in your build) - the IF frequency is therefore limited to be in the passband of these filters.? The SI4432 does some more DSP filtering internally.
The #define statements shown in your pictures are not for the low mode sweep but for the test modes for the SI4432 FIR filters and the SAW filters.
The low input is filtered by the 350Mhz low pass filters.? These are there to avoid alias products, and also to make the output in signal generator mode fairly clean.
In the high mode the signal goes directly into the SI4432 with no external filtering.??
Remind me of the issues you have with unclean traces - in high mode, low mode or both???
Dave M0WID
