Using a base/generic type class as a parameter in a method

I am trying to use the implements of PHP where the parameter is a base/generic type class.

BaseFormRequest.php

class BaseFormRequest extends FormRequest
{
... methods here
}

StorePostRequest.php

class StorePostRequest extends BaseFormRequest
{
... methods here
}

IController.php

interface IController
{
    public function store(BaseFormRequest $request);
}

class PostController extends Controller implements IController
{

    public $service;

    public function __construct(PostService $service)
    {
        $this->service = $service;
    }

    public function store(StorePostRequest $request)
    {
        $post = $this->service->store($request);
    }
}

As you can see in the code:

1. in StorePostRequest, it extends the BaseFormRequest.
2. in the IController, the parameter in store method is type BaseFormRequest.
3. in PostController, the parameter in store method is type StorePostRequest.

I am getting the error

Declaration of PostController::store(StorePostRequest $request) must be compatible with IController::store(AppHttpRequestsBaseFormRequest $request)

What I do know is that

1. if I remove the implements IController, the code works as intended
2. if I change the PostController@store param to BaseFormRequest, or IController@store param to StorePostRequest the error is fixed, but I cant customize the rules in each model this way.

Is it not possible to use a generic class in interface so that when I implement it in my controller, I can use the correct class that extends to the generic class?