Joseph, I think you are referring to Moed Katan 25a, which tells us that Rebbi Aba said at the funeral of Rav Huna that "our rebbi was worthy that the Shechinah should rest upon him, but Bavel was the cause that it did not."

However, I think this is not a Stirah to Megilah 29a, where Rav Sheshes felt the Shechinah in the synagogue, because a synagogue anywhere in the world is like Eretz Yisrael and the Shechinah is present there.

The source for this is the Gemara in Berachos 8a which tells us that they said to Rebbi Yochanan that there are old people in Bavel. Rebbi Yochanan was perplexed when he saw old people in Baval, because we say in the second paragraph of the Shema, "so that your days should be long, and the days of your children, on the Land." This suggests that we are promised long life only in Eretz Yisrael, not in Chutz la'Aretz. However, when they told Rebbi Yochanan that the elderly people in Bavel go early in the morning to the Beis ha'Kneses and stay late, he said that this is what helped them to live a long life.

The Maharsha there explains that the Batei Kneses in Bavel will, in the future, be established in Eretz Yisrael, as stated in the same Gemara in Megilah 29a that you cited, Joseph. Because in the future they will be established in Eretz Yisrael, it is as if they are already a part of "the Land" so people who go there merit long life.

We learn from this that if you are in a Beis Kneses in Chutz la'Aretz, it is the same as being in Eretz Yisrael. That is why Rav Sheshes felt the Shechinah in the synagogue in Bavel. Rav Huna also felt the Shechinah when in a Beis Kneses in Bavel, but outside the Beis Kneses the Shechinah could not rest upon him.

Kol Tuv,

Dovid Bloom