The answer to what really mostly changes the effects is terpenes and cannabinoids.
Sam the Skunkman wrote about smoking an afghani and a thai with identical cannabinoid profiles almost. Dramatically different terpenes. The effects were dramatically different in his own words. And we all know what Thai and Afghani is supposed to be like.
The ratios indicated by seed companies are totally useless. Some plants will have different %'s of those genetics. What they're basically saying is it's mostly composed of indica leaning varieties. But indicas can be uppity too if they have the right terpenes.
Cannabinoid differences can obviously have a large effect as well. The Skunkman seems to think that when dealing with high THC varieties, the terpenes are the most important factor though. Considering his history, and his resources, he's worth listening to IMO.