frequency response - Berchin's FDLS arbitrary filter design algorithm

I'm trying to use Berchin's FDLS methods (for those that don't know what it is, it's a way to design arbitrary magnitude and phase of an IIR Eq)

I tried different things but neither gave me what i asked:

1. 
   

   I tried to design an allpass filter with arbitrary phase response (nothing fancy just a linear phase and a short deviation for 5 points) and it didn't worked as planned. Actually what i want to do is to counter the phase change of an IIR filter

   
   


2. 
   
   

   I tried a linear phase response for a $-12\textrm{ dB}$ notch and the same way it didn't worked (in black the desired response)

   
   

   

   
   

   I used a samplerate of $316$, $M=158$ points and a filter order of around $50$.

   
   

Do I need to use more points to increase the filter order or is it just impossible to design my filters using that algorithm?