Rigol DG-1022Z function gen. Can FM frequency track main frequency?

[Circlotron]

Looking at possibly getting Rigol DG-1022Z function generator. One thing I want to do with it is generate a 100Hz square wave and frequency modulate it at 12.5Hz from the second channel. Then when I wind the 100Hz frequency up and down a bit can I have it so the modulation frequency from channel 2 tracks channel 1 in a ratiometric manner. That is to say, if I increase channel 1 frequency from 100Hz to 150Hz can channel 2 automatically follow from 12.5Hz to 18.75Hz?

The purpose of this is to simulate an optical encoder reading a slotted disc that is not perfectly central on a rotating shaft to see how well some software tolerates this imperfect signal.