Using and overriding variables in ConfigMaps?

[ArthurSap]

I'm trying to use variables in the ConfigMap of my base overlay, variables which will be set differently in each overlay.
The folder structure is something along the lines of:

.
├── base/
│   ├── service_a/
│   │   ├── kustomization.yaml
│   │   └── service-a-configmap.yaml
│   ├── service_b/
│   │   └── ...
│   ├── kustomization.yaml
│   └── base-configmap.yaml
└── overlays/
    ├── dev/
    │   ├── kustomization.yaml
    │   └── dev-configmap.yaml
    └── prod/
        └── ...

I will describe more-or-less each relevant file to explain my question better:
service-a-configmap.yaml:

apiVersion: v1
kind: ConfigMap
metadata:
  name: service-a-configmap
data:
  FOO_VAR: "something-$(BAR_VAR)"

--
base-configmap:

apiVersion: v1
kind: ConfigMap
metadata:
  name: base-configmap
data:
  BAR_VAR: "per-overlay-$(ENV_NAME)-stuff"

base/kustomization:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

vars:
- name: BAR_VAR
  objref:
    apiVersion: v1
    kind: ConfigMap
    name: base-configmap
  fieldref:
    fieldPath: data.BAR_VAR

resources:
- base-configmap.yaml
- ./service-a
- ./service-b

When I run build in the base folder, the result is as expected:

# Result in service-a-configmap
FOO_VAR: "something-per-overlay-$(ENV_NAME)-stuff"
...
# Result in base-configmap:
BAR_VAR: "per-overlay-$(ENV_NAME)-stuff"

I want to replace the $(ENV_NAME) with a different value in each overlay.
dev-configmap:

apiVersion: v1
kind: ConfigMap
metadata:
  name: dev-configmap
data:
  ENV_NAME: "dev"

And when running build from the dev overlay, my desired result is:

# Result in service-a-configmap
FOO_VAR: "something-per-overlay-dev-stuff"
...
# Result in base-configmap:
BAR_VAR: "per-overlay-dev-stuff"

But what I get is:

# Result in service-a-configmap
FOO_VAR: "something-per-overlay-$(ENV_NAME)-stuff" # <-- nothing changed
...
# Result in base-configmap:
BAR_VAR: "per-overlay-dev-stuff" # <-- changed as expected

Here's the dev/kustomization I'm trying to use:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

vars:
- name: ENV_NAME
  objref:
    apiVersion: v1
    kind: ConfigMap
    name: dev-configmap
  fieldref:
    fieldPath: data.ENV_NAME

configurations:
- configuration.yaml # (contains only `varReference`  with {kind: ConfigMap, path: data})

resources:
- dev-configmap.yaml
- ../../base

What am I missing? Is this even possible?

There are 14 services in the base overlay, there are 13 values in the base-configmap that contain the $(ENV_VAR) (and other 2 similarly used variables), these values are used in most services (mostly as values in their respective ConfigMaps).
I don't think replacements is a good fit for my use-case.
I tried using patches in the dev overlay (by changing the name of the ConfgiMap to base-configmap too) to no avail.