Here is the case:
adduser pravdomil www-data
adduser tana www-data
touch /home/test.txt
chown pravdomil:pravdomil /home/test.txt
chmod 440 /home/test.txt
reboot
runuser -l tana -c 'cat /home/test.txt'
Produces cat: /home/test.txt: Permission denied
on Ubuntu 16.04.1 LTS
The file is readable by group and if two users is in the same group (and one is the owner of file) both should have read access?