Even if Qunari were large everywhere, Dwarven women have bigger hips than elves or humans (don't know about Qunari women) so I could see them being appropriately accommodating.
Alright, I have some biological speculation that hopefully doesn't verge into wildly inappropriate. Being as clinical as possible, here. Mostly because I've seen "size" used as some grounds for why Qunari shouldn't be with anyone. *eyeroll*
For the most part, Qunari are almost completely identical to humans, except for their horns and weird skin color and claws. If we presume that their sexual organs are similarly proportionate to humans, we can scale in relation to size. Qunari seem to be around seven feet tall, approximately. The average human male of the US is roughly 5'10", or 70 inches. At 7' the average Qunari male would be 84 inches. 70/84 is 83.3%, so "size" would only scale by roughly 17%. Considering the wide variation in the size of junk even among humans, I highly doubt Qunari/Anyone coupling would be anatomically impossible. There are also other matters to discuss regarding the elasticity of lady junk, given the ability to give birth/proper partner accommodation, but we won't go into that. XP
A real world example could easily be some of the monstrous basketball players and their respective SOs.