Surely when evaluating distance learning a big factor in passing or failing is how long you are going to beaver away at home getting up to speed on things before you attend the brush up course.
I can't see that 2 or 3 modules really comes into it unless you can somehow compare experiences between different people at different schools who studied the same amount and had the same intellect and aptitude to study. In reality this is impossible so again it will be one of those things that is down to the individual and your own personal circumstances.
Rather than the number of modules I would be more interested in checking how the schools split the subjects as there is a significant amout of overlap in certain areas. POF and Perf are two good examples.