When do you leave out the preposition in a relative clause?

A non-fiction titled "Do the Right Thing" published in 1998 has this sentence:

(1) Am I treating this stranger with the same consideration that I would a friend?

Another book (fiction) titled "Strong Rain Falling: A Caitlin Strong Novel (by Jon Land)" published in 2013 has this sentence:

(2) ...and treat the enemy with the same consideration with which they had treated the residents of Willow Creek.

Are both these grammatical and natural English?

If so, it seems to me that the that clause of (1), as well as the which clause of (2), is a relative clause. And that in (1) the preposition with has been left out of the relative clause.

Assuming that both are correct English, my question is why (1) is possible without the preposition with stranded at the end? (Edit: Is it because the relative clause of (1) lacks the lexical verb "treat"?)

Also, if preposition stranding is possible with these relative clauses, are these possible English?

(1a) Am I treating this stranger with the same consideration that I would treat a friend with?

(2a) ...and treat the enemy with the same consideration which they had treated the residents of Willow Creek with.

Edit: Here is another example without ellipsis, and it's taken from a hospital website in England:

(3) We Ask That Our Patients:

treat our staff with the same consideration that you would expect to be treated yourself. Violent, abusive or intimidating behaviour of any kind will not be tolerated and will lead to immediate removal from the practice list.

Now, should the editor of the website have added with at the end of the boldfaced portion?

Revamp: Since there has been some confusion due to ellipsis in (1), I would like to give this question a revamp.

After reviewing the answers and comments so far, I have concluded that the omission of "with," along with that of "treat," in (1) was simply due to ellipsis, and that the boldfaced clauses in (1), (2), (1a), (2a) and (3) are all relative clauses. (Any criticism would still be welcome as to any part of these conclusions.)

So let's forget about (1) and focus only on non-elliptical examples, i.e., (2), (1a), (2a) and (3). The issue now is whether, in each of these non-elliptical constructions, "with" is redundant, essential, or optional, on the meaning of which I will elaborate in the following three scenarios:

Scenario A: If it's redundant, (2), (1a) and (2a) will be ungrammatical, and only (3) will be grammatical.

Scenario B: If it's essential, (3) will be ungrammatical, and (2), (1a) and (2a) will be grammatical.

Scenario C: If it's optional, (2), (1a), (2a) and (3) will all be grammatical.

Which is the right scenario and why?

Edit: For those who support Scenario C, please elaborate on what it is in these examples that renders optional the use of preposition "with", when in general you are not to leave out a preposition from a relative clause if that preposition is part of the relative clause.