Paragraph block preset names and font sizes

Themes use different names, and different font sizes, for the paragraph block presets.

For instance, If I change from the default Twenty Twenty theme to GeneratePress theme. And I already have Paragraph blocks I built using the preset options in Twenty Twenty theme.

That text can look much bigger in GeneratePress than it looked in Twenty Twenty theme.

Is there a standard way to switch themes. And to keep font sizes similar in the GeneratePress blocks, to how they looked in the Twenty Twenty blocks?

I'm not talking about paragraphs in general.

Just paragraph blocks that use preset names to change the font sizes.

Thanks
Philip.