[exim] Ubuntu 20.04 and CONFDIR

I've been trying to get exim4 up and running on Ubuntu 20.04.

There is the standard:

# Macro defining the main configuration directory.
# We do not use absolute paths.
.ifndef CONFDIR
CONFDIR = /etc/exim4
.endif

which is a little confusing because it says "We do not use absolute paths."
then it uses an absolute path.

But the problem is, it doesn't appear that CONFDIR is being honored. Later
in the config file there is:

.ifndef MAIN_TLS_CERTIFICATE
MAIN_TLS_CERTIFICATE = CONFDIR/exim.crt
.endif
tls_certificate = MAIN_TLS_CERTIFICATE

.ifndef MAIN_TLS_PRIVATEKEY
MAIN_TLS_PRIVATEKEY = CONFDIR/exim.key
.endif
tls_privatekey = MAIN_TLS_PRIVATEKEY
.endif

But those are NOT being defined.

# exim -bP | grep tls
tls_advertise_hosts = *
tls_certificate =
tls_crl =
tls_dh_max_bits = 2236
tls_dhparam =
tls_eccurve = auto
tls_ocsp_file =
tls_on_connect_ports =
tls_privatekey =

etc...

if I manually put:
tls_certificate = /etc/exim4/exim.crt
tls_privatekey = /etc/exim4/exim.key

at the top of:
/etc/exim4/exim4.conf.template or /etc/exim4/exim4.conf.localmacros

then they get assigned. but there are a bunch of other things not being
configured that are depending on CONFDIR. I've tried everything I can
think of to make it work and it just doesn't.

Any pointers would be greatly appreciated.

Thanks in advance,
Elliot