After a quick look at the code, it seems that the global used size is saved in XenForo_Application::get('options')->attachmentThumbnailDimensions
And this size is used in the attachment model and in the defered script to rebuild the thumbnails
What if i want to have different thumbail sizes?
e.g. my Gallery thumbails should be 200x200, my post thumbails only 150x150 and my cms thumbails 250x250
If the data would come from the attachment handler, it would be much easier to use different sizes for the thumbails.
You could even add the attachment handler name / content ty eas parameter to attachmentModel::getAttachmentContraints, which could return then the content type specific attachment sizes. so we wouldn't have to implement / overwrite this method for own types