> でもほんとに、エピソード21 **に** は涙が出るほど笑ったよ。

For some reason I feel like it would be better without the に (in bold) but I
can't explain why.

Another person said that で would be better but I think that it changes the
meaning completely. I mean that （登場人物の）Aさんは エピソード21では涙が出るほど笑ったよ would be okay
but if the subject is not a character of the episode で is not appropriate.

Could you explain the reason behind using に here?
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2018-09-26T20:19:55.393
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2018-09-26T20:19:55.393
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question
particle-に particle-で に-and-で
Why is に used in that sentence?