I've looked into this further and it looks like my float values are indeed too big - I did not realise that float numbers allow only up to 9 significant decimal digits and my values have more than that.
It threw me off because on ES and Kibana I can still see the values represented correctly, i.e. the values do not look rounded on Kibana. Both double and float values look the same so I naturally expected the comparison / range query to work the same for both. I got bamboozled again.
