Custom block lighting problems

Hi, I have some problems with the lighting of custom objects created with workbench (jason model). Basically objects that are more than a block away from a light source become brutally darker, unlike minecraft blocks, on which the light gradually decreases. The image below shows the difference between different types of blocks.

In the next photo you can see the effect it has on more distant objects.

Also, if an original minecraft block is placed on a custom object, the top faces turn black.

Do you have any advice to solve this problem or is it a limitation of MCreator?

Thanks in advance for your reply.