I don't understand this shaketune graph

Hi,

I'm building a ratrig vcore 4 which is a core xy printer, I've used shaketune to measure the belt tention but I'm facing a case which isn't covered by the documentation.

doc : https://github.com/Frix-x/klippain-shaketune/blob/main/docs/macros/compare_belts_responses.md

https://preview.redd.it/6mknie893zod1.png?width=800&format=png&auto=webp&s=c10d5758d1542fe2b5c445faf410a8996bfc5c22

Isn't it weird, left peak the yellow is lower and right peak the blue one is lower.

What could this indicate?

Thanks.