Sorry, we posted simultaneously and I didn’t see your second message.
Without knowing what you’re doing to crop and warp the texture, it’s hard to know – but it sounds as if doing whatever you’re doing between calls to -bindToDrawFrameOfSize: (passing the size you’d like to SyphonServer to send images as) and -unbindAndPublish might work – otherwise perhaps if you share some more code we can give more precise pointers.