The EF400 is an interesting product unfortunately let down by a few design flaws and oversights.
If you’d like to see full measurements they are posted here: https://headphones.com/blogs/reviews/hifiman-ef400-review-measurements
Product Page: https://headphones.com/products/hifiman-ef400
Where did you confirm this?
Why it is not stated here?
https://audiophilestyle.com/forums/topic/67647-new-hifiman-ef600-dac-headphone-amplifier-with-himalaya-r2r/?do=findComment&comment=1234257