merge yaml config section and host config

[huiyang]

version of deployer: 7.3.0
I have something like the following in my deploy.yaml file

config:
  directadmin:
    domain_name: example.com

hosts:
  host1:
    directadmin:
      db_name: host1_db

i expect both "directadmin" sections will be merge when i get('directadmin') under host1 execution, but it have only have db_name key in $config['directadmin'].

how can i merge them? is that possible?
(i have like 10 hosts, so not prefer to copy the whole section to the host section.)

thanks.