Laravel Nova MorphOne - set default fields based on relation

I am using the MorphMany and MorphOne relationship types to define addresses and a primary address for multiple models, a given model can have many addresses, but only one primary address.

I also require that when a model is created that has addresses, the primary address be created at the same time, which means I use the MorphOne field and make it required on the resource.

This works just fine. However, on my Address model, I have the property: is_primary. What I need to do is set is_primary to be true by default IF the address being created is the primary address, and set to false otherwise. But when using Nova, if I check to see if the Address is being created viaRelationship, I get the underlying morphMany relationship of addresses not primaryAddress.

So, how do I get the Address resource to recognize if the creation form is being displayed in the context of the MorphOne field instead of just a normal creation field?

Example resource that has addresses:

public function fields(NovaRequest $request): array
    {
        return [
            Text::make('First Name'),
            Text::make('Last Name'),
            BelongsTo::make('Type', 'type', TrainerType::class),
            MorphOne::make('Primary Address', 'primaryAddress', Address::class)
                ->required()
                ->onlyOnForms(),
            MorphMany::make('Addresses', 'addresses', Address::class)
                ->onlyOnDetail(),
        ];
    }

Address resource:

    public function fields(NovaRequest $request): array
    {
        return [
            Text::make('Address Line 1'),

            $this->getIsPrimaryField($request),
        ];
    }

    protected function getIsPrimaryField(NovaRequest $request)
    {
        //$request->viaRelationship only ever shows 'addresses', not 'primaryAddress'
        if ($request->viaRelationship === 'primaryAddress') {
            return Boolean::make('Is Primary')
                ->default(true)
                ->readonly()
                ->withMeta([
                    'extraAttributes' => ['readonly' => true],
                    'value' => true
                ]);
        }

        return Boolean::make('Is Primary')->default(false);
    }