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?
