Firstly $12 is not a lot for getting any metrics. You have very high cost for engagement, if its a mobile game I would stick to just mobile traffic. It seems to me you are following whats the hottest trend in the highest GEO's which could be why you are paying so much. From what I learnt from Zeno is that to make any money with a small budget target the smaller areas of the market.
Doing this kind of campaign for mobile is not quite optimal. Do mobile install ads and try to target as less as possible as that might decrease the final price. Use creatives that reflect the gameplay well and you should have much better results. Keep in mind FB is over-reporting mobile installs for about 30% so you need to check with the client what is the actual number of installs
Any update on this ?