Hi! I have a 22lb dog who is right in between the XS and S sizes with the Ruffwear Approach Pack. The XS fits a little tight (1 finger in between strap and dog) on the loosest setting... the S fits a tad bit loose on the tightest setting (3 fingers in between dog and strap)... Do you have any advice on which to use? I don't want him to chafe with the larger one, but want him to not be too constricted with the XS. Thanks for any advice you can provide!