How does Riot determine what XPO's they go to?

How does Riot determine what Fan XPO's and Comic Cons etc they attend to? For example, a new and very rapidly growing Comic Con in Kelowna BC has 2 cosplayers that have even been featured by Riot attending, but when would Riot themselves determine going to events like this? Does it have to reach a certain size/popularity etc?

I've been a fan of League since it launched, especially since I heavily played the pre League of Legends existence of the WC3 mod that spawned this game. If I remember correctly, some of the creators of that mod founded Riot. However I've never seen Riot at any of the XPO's close enough to home for me to get to meet them, but this new XPO is definitely close enough.