Get observation compartment number from model
Details
For ADVAN1-4/11-12 this is easy, for other ADVANs we have to make some assumptions based on whether scaling parameters have already been defined for the model. Logic is as follows:
if S1 is defined and not S2, assume it's 1.
if S2 is defined and not S1, assume it's 2
if both are defined, assume it's 2 but show a warning
if none are defined, assume it's 2 but show a warning