Thats because of the MLCCs you are considering, you can get ones with different voltage coefficents if you want. Like ones that keep 95% at 100v or even better. They cost more and have different materials.
I was once caught by this issue too. The problem was that I didn’t know about the basic phenomenon (MLCC losing capacitance with voltage) so I didn’t know that I was expecting extreme parts.
Extreme parts cost a whole lot more