Tapas on my phone gives me visual real estate of 12cm by 7cm. At that size the font size you used to start off with does the job.
BUT~! I grew up reading comics with dense text blocks and not the...
... padding that defines the Webtoon format. I can parse what you wrote, but you main audience might not be able to.
Both Tapas and Webtoon push big text with minimum words for a reason so going larger will only help you.