Despite a bunch of answers on stackoverflow for the best way to set the umask for Apache and/or php-fpm Ubuntu the only approach that I found to really work in Xenial was to modify the Systemd service configs (because Apache etc inherits its umask from its parent process).

From the Ubuntu wiki the best way to do this was using drop-ins:

Systemd allows a similar facility via "drop-ins": a drop-in allows a directive to be modified without changing the original unit file. To create a drop-in:

Create a subdirectory below either "/etc/systemd/system/" or "/lib/systemd/system/" called "${unit}.d/".

Create files called <something>.conf in the "${unit}.d/" directory containing the directives that you wish to override. 

Within the drop-in e.g. “/lib/systemd/system/apache2.service.d/gimme-mods.conf” I could then simply set the Umask within the [Service] chapter to be: