The difference between "poetic" and "poetical" in usage

I came across a sentence on grammarist.com:

Blest is an archaic form that shows up mainly in references to old, mostly poetical texts and as a poetic affectation.

I find the alternation between the two words poetic and poetical interesting. Between the pair, poetic is of course much more common. According to ODO, poetical is defined as

Relating to poetry.

Written in verse rather than prose.

Having an imaginative or sensitively emotional style of expression.

And the definitions of poetic are, well, quite similar if not the same:

relating to or used in poetry.

written in verse rather than prose.

having an imaginative or sensitively emotional style of expression.

I found a discussion on Word Reference Forum which doesn't have much information but rather makes the topic more confusing.

How do they differ in usage? What is the rationale behind the alternation of words in some texts, e.g. the Grammarist post.

Solution 1:

• Ode to Autumn rang the curtain on the poetical career of John Keats as he stopped writing because of his failing health.

In the above sentence, it is not possible to replace the adjective 'poetical' with 'poetic'.

The difference between the two words is that while both are adjectives obviously referring to poetry, 'poetic' refers to the poetry itself whereas 'poetical' can also refer to associated meanings beyond poetry proper. For example these sentences:

• He described the incidents poetically.
• He was poetical in describing her beauty.

Here, the sentences do not mean he spoke in verses but his speech mesmerised us as if we were listening to a soulful redition of a good poem.