Dependency management

[andromeda306]

I need some help sorting out how best to approach dependency management when using stacks. I understand that currently dependency relationships need to be defined as the unit level, but I'd like some guidance on how it should be achieved in regards to the following 2 scenarios:

1. internal dependency - where I am deploying a resource in eu-west-1 which is dependent on another resource in eu-west-1.

.
├── live/
│   └── dev/
│       ├── eu-west-1/
│       │   ├── region.hcl
│       │   └── terragrunt-stack.hcl
│       ├── us-east-1/
│       │   ├── region.hcl
│       │   └── terragrunt-stack.hcl
│       └── environment.hcl
├── stacks/
│   └── main/
│       └── terragrunt.stack.hcl
├── units/
│   ├── unit1/
│   │   └── terragrunt.hcl
│   └── unit2/
│       └── terragrunt.hcl
└── root.hcl

In this case unit2/terragrunt.hcl should contain the following, if it is dependent on unit1/terragrunt.hcl

dependency "unit1" {
  config_path = "../unit1"

  mock_outputs = {
    public_subnets = ["value-12345678"]
  }

  mock_outputs_allowed_terraform_commands = ["plan", "validate"]
}

inputs = {
  myvalue = dependency.unit1.outputs.foo
}

2. external dependency - where I am deploying a resource from us-east-1 which has a dependency to a resource in eu-west-1.

.
├── live/
│   └── dev/
│       ├── eu-west-1/
│       │   ├── region.hcl
│       │   └── terragrunt-stack.hcl
│       ├── us-east-1/
│       │   ├── region.hcl
│       │   └── terragrunt-stack.hcl
│       └── environment.hcl
├── stacks/
│   └── main/
│       └── terragrunt.stack.hcl
├── units/
│   ├── unit1/
│   │   └── terragrunt.hcl
│   └── unit2/
│       └── terragrunt.hcl
└── root.hcl

In this case, running a similar setup from us-east-1 results in the error Error processing module at './.terragrunt-stack/unit1/terragrunt.hcl'. How this module was found: dependency of module at './.terragrunt-stack/unit2'. Underlying error: file does not exist - understandably, as .terragrunt-stack/unit1/terragrunt.hcl only exists in the eu-west-1 directory. What is the best way to approach a setup like this?

I have attempted to process what was said here #3313 (comment) but it just hasn't clicked.