Some airlines have very little YQ surcharge, thus the fare is higher, others have very high YQ and other surcharges which is unbelievable. On LH group airlines, for award tickets, the taxes are higher than the lower economy revenie tickets, on top of that you have to burn many thousends of miles. Singapore airlines charges just airport taxes for flights to South east Asia and Australia, which are less than 100 euros, on other hand, other many charge 900 euros!
SFO-FRA is not the same as FRA-SFO, naver has been, the same applies for many countries. MAD-EZE on Iberia is almost 50% cheaper than the other way around. You can always buy SFO-FRA in business and than add FRA-WAW in lower economy for 110eur more or 400 eur in cheapest business. That would be much cheaper than buying SFO-WAW via FRA on the same ticket.
The pricing policity is insane, I will never understand how BCN-ZRH on direct flights with LX costs more than BCN-FRA-IST or BCN-ZRH-GVA (4 flights)... and inter Swiss flights are almost 120 CHF one way,
If you have time, you can check several different options and buy the cheapest one, even if that means buying several tickets on different fares and airlines!