Sebastien Thanks for testing out the plugin and the detailed results. Always great to get more feedback / use cases.
I have another update coming which is more focused on making multiple instances of the same skeleton (but optionally different skins) more efficient (reuse Spine atlas texture.)
For the PMA, the intention is that if you exported with PMA, then you would check that property, but if you did not, you would uncheck that property. If your export and the property don't match, there may be artifacts, which is expected.
For the bounds and scaling, so far this has been a tough issue to solve directly. Since we are rendering to a texture to integrate the Spine character more fully into the C3 renderer (e.g. we can apply effects, C3 scaling, rotation, Z order, etc.), the size of the texture we render into is generally set once. A work around for now is to add a blank image / rectangle in Spine (e.g. w/ 0 opacity) which will cover the size of the area that the animation moves in. Then the plugin will scaled the texture to that size. I know it's not perfect, but works for me so far. I would also animate any large translations / movement by using C3 events to move the Spine character, but do the in place animation in Spine (e.g. with a big jump.)
If you are able to add the bounding box rectangle, you should be able to set the Spine scaling to 1.0 and then if your C3 project filtering is set to nearest, the pixel art may be cleaner.
If you can share you sample project/character, it would help me debug / test on my side.
You can contact / DM me the project on the Construct Community Discord if you can share it (Mikal is my username their also).