Following feedback from the community (thanks to all who contribute regularly!), the warp core logic has been changed.
Now each added pearl will fill the core existing pearl or create a new pearl of the grid scale used.
Which means that adding a small pearl will only partially fill an existing pearl or create a new partially filled one.
Likewise adding a large pearl might adds several pearl to the core.
In short there is now disadvantage of using larger grid size warp core when it come to actual fuel capacity.

Thanks for playing!