In the end the best solution I found was to define EL_REFLECTED_EXPANDED_FIELD like this

deferred class
	EL_REFLECTED_EXPANDED_FIELD [G]

inherit
	EL_REFLECTED_FIELD

	EL_SHARED_ONCE_STRINGS

feature -- Access

	value (a_object: EL_REFLECTIVE): G
		do
			enclosing_object := a_object
			Result := field_value (index)
		end

feature -- Status query

	is_expanded: BOOLEAN
		do
			Result := True
		end

feature -- Comparison

	are_equal (a_current, other: EL_REFLECTIVE): BOOLEAN
		do
			Result := value (a_current) = value (other)
		end

feature {NONE} -- Implementation

	field_value (i: INTEGER): G
		deferred
		end
end

Then class EL_REFLECTED_BOOLEAN for example, can implement `field_value' like this: 

class
	EL_REFLECTED_BOOLEAN

inherit
	EL_REFLECTED_EXPANDED_FIELD [BOOLEAN]
		rename
			field_value as boolean_field
		end

It finalizes well and conforms to my original intention.