How to add more analytic conditions to a curve fitting operation

Dear everyone, I am dealing with a particular thus embarrassing problem. I would like fit some experimental measurements with the fllowing analytical function:

g = fittype(@(b,a,x) (a+b-a*b*sin(x))./(a*b+1-2*a*b*sin(x)));

However I would like to add some precisions regarding the real values of a and b. Both a and b are real and positive. In my case b always obeys to this relationship: 0<b<1. Then depending on the experimental case I would like to precise one of those 3 following options: 0<a<b OR b<a<1 OR 1<a<1/b

I have sadly found no solutions regarding my specific problem.

At present my fitoption parameters are the following ones:

               s = fitoptions('Method','NonlinearLeastSquares',...  
               'Lower',[0,0],...   
               'Upper',[1,1],....                  
               'Startpoint',[sa sb],...         
               'Normalize','off');       
               sa=0.5;    
               sb=0.5;

Do you have any idea to complete the fitoption fields so that I can satisfy my request?

Thank you very much for your help.

Nono