Nice, always good to see another implementation! Were you able to get past the pivot alignment issue? Because in a proportional font, the word seems to slide around your eye as it shifts the spacing of the characters immediately adjacent to the pivot, so I anchored the pivot character and allowed the rest of the word to extend freely from both sides.

What stood out to me as a major difference was pacing though - a flat interval makes for a pretty robotic reading experience since there's no sentence structure, and I found that using multipliers on the base duration was more effective, getting about 3x for sentence ending punctuation, 2x for commas, and a little extra for long words overall was more noticeable than any other adjustments I made.

I'm curious if DuoBook is actually trying to implement reading in a second language as a learning tool as the name suggests, and if so, how does that affect things? I would imagine the pacing would be overall lower (particularly for punctuation) and recognition of the words you're actually reading would have more impact on comprehension than the ones you're just learning to read.