What Causes Low Germination Rates?

What causes low germination rates of flasked orchid seed?

Is a low seed germination rate most often due to too little pollen in
contact with the stigmatic surface at pollination time?

I would suspect that different media formulae would produce different
results for a given cross.  Has anyone had any experience with this
phenomenon?  Any specific media recommendations for reed-stem
Epidendrums?

How big a factor are temperature, day-length and light levels?

Are intergeneric crosses more likely to have low germination rates?

It is a ~10% germination rate of Epidendrum atacazoi*** (bifalce)
selfed that prompts my question.

It's a simple question, but I suspect the answer will be complex.