No shoe is supposed to fit either too tight or too loose. We recommend that your Chacos are snug enough and that you always allow enough room to get your finger underneath the piece of webbing.
For the sandal with the toe loop, you want to make sure that you don't overtighten that toe loop. That's something you can always adjust as you wear it, but you just want to make sure there's still a little bit of movement down in that area as well.