Yes, you’re right, John; and thank you for your kind words.
“Within you” was the traditional English interpretation, adopted by the King James translators. But that’s no guarantee of accuracy. Oddly, because of more recent archaeology and the access we now enjoy to more manuscripts and a more well-rounded understanding of ancient cultures, we’re in a better position to interpret the Greek texts than the scholars of 1621, even though we’re farther removed from the events.
We now know that “in the midst of you” is a valid possibility, but the traditional interpretation is still valid as well. So, Bibles translated by people with a conscience show both translations: they pick one to put in the body of the text, and make a footnote to show the other. If you come across a translation that doesn’t present both options, throw it in the trash — the translators are opinionated and unwilling to accept their own fallibility. :-)
Here’s the thing that I find interesting: both possible translations are consistent (1) with scripture, and (2) with the words of Jesus. Jesus talked about the ekklesia — the church, the assembly — and there’s no particular reason to discount the presence of the kingdom of God in the assembled body, as you referenced in Matthew 18:19–20: “Again I say to you, if two of you agree on earth about anything they ask, it will be done for them by my Father in heaven. For where two or three are gathered in my name, there am I in the midst of them.” The Apostle Paul also wrote about this: “So we, though many, are one body in Christ.” (Romans 12:5)