Bioequivalence and Bioavailability Forum

Hello everyone!
I am a beginner on the subject about IVIVC and I have plenty questions. Can somebody help me?
Coul you recommend me a step by step course to develop ivivc?

I´m trying to develop an example of IVIVC. I have in vitro and in vivo data for an intermediate release (InR) formulation, a slow release (SR), immediate release (IR) and the reference formulation (target). I only have in vitro data of the “test” formulation and I wan to predict its pharmacokinetic parameters. I tried to do it but something was wrong (see images below).

1. I read in a forum that UIR depends on the number of compartments, but what exactly does it mean? Should I always put 3?
   
2. In the validation which one should I put as external or internal?
   
3. How do I know if I should put the weibull function or the double weibull function (for example)? Is the fit bond performed before or does the software also perform it?
   
4. For weighting, how do I know which one to choose?

My apologies, I think there are many questions, I hope you can help me with some. It is very important for me.

Thaks
Best regards