Robust control problem with parameter variations

I would like to know which extreme variation in the parameters of a t.function H(s) would still satisfy this relationship:

Below is the explanation and problem formulation

s=tf('s')

r=tf([1 4.1 4.4],[1.17 29.63 7.33])

freq = logspace(-1,1,100);

%transfer function L

L =(5.05*s + 6.312)/(s^3 + 4.084*s^2 + 6.566*s)

%transfer function H

H = (1.5247e05*(s+1.25))/(s*(s+2)*(s^2 + 6.86*s + 24.01)*(s^2 + 94.5*s + 3969))

[magH,phaH]=bode(H,freq);

magH=squeeze(magH)';

[magL,phaL]=bode(L,freq);

magL=squeeze(magL)';

Res=abs((magH./magL) -1)

semilogx(freq,Res)

hold on

r=tf([1 4.1 4.4],[1.17 29.63 7.33])

[magg,phasee]=bode(r,freq); mag=squeeze(magg)';

semilogx(freq,mag);

This is the result for the nominal case:

Now, with the uncertain parameters

%Uncertain parameters

k= ureal('k',1.5247e05,'Percentage',100); a= ureal('a',6.86,'Percentage',100); w= ureal('w',24.01,'Percentage',100); b= ureal('b',3969,'Percentage',100); c= ureal('c',94.5,'Percentage',100);

%Uncertain transfer function

H = (k*(s+1.25))/(s*(s+2)*(s^2 + a*s + w)*(s^2 + c*s + b)

I would like to know the largest combination of the variation of the uncertain parameters in H(s) would make the

left side of the equation(given by the blue line) equal to the right side of the equation(red

envelope):

I would like the blue line to just touch the red line for the frequency range

I had tried using robuststab and robustperformace from the robust control toolbox but it is not satisfying the condition.

Hear from you people!