I think slushpool if you are comparing your present hashrate to their dashboard its not inaccurate but base on what i heard its not affecting your earnings..
If you still not satisfied better to ask slushpool in their official thread they can gives you more insight about your issue..
https://bitcointalk.org/index.php?topic=1976.22660

If you really wanted to earn higher  i suggest to go kano pool and the pool fee is 0.9% which is great.. they pay higher than other pool base on what i experienced..
Check it here https://bitcointalk.org/index.php?topic=789369.0