Our plugin adds the play icon with the correct size to the image. However, social media sites can change the resolution of the image in the link preview, and the size of the play icon will also be changed with that. If you check the images you have shared, not only the play button, but the size of the whole image is different. It has a wide resolution which is making the play button small.
Hope that helps and please do not hesitate to let us know if you need our assistance with anything else.
