Cloudfront high % misses

A customer mentioned that they are seeing increased latency from Europe as compared to US. They have: CloudFront -> S3 origin (in us-west-1). Requests are over HTTPS using signed URL. Using Default Cache Behavior

Looking at their Cache Statistics Reports, we noticed that Europe had 52% Cache Miss in the last 2 weeks.

1. I am trying to see if there is a way to validate that the high % misses are valid. i.e, requests were made for different objects and so didnt get cache benefit.

2. The objects are modified only once a week, hence the customer wanted to check if increasing the TTL will help. Since the requests are signed URL I don't think it will help, but wanted to check here.

Thanks!