Second belly strap is super close to his *. All areas of contact are adjustable. Second strap lands geographically across my boys.
Small won't fit a jack russel. The back strap is inconvenient.
French bulldog has one and now my frenchie does as well. The adjustability is excellent, but the real key is the quick release front clip. We have a 100lb rottie and this works well for her.
The portion of the harness that is on the dogs chest is not long enough, even with all of the straps opened up all the way. The harness is too short for the dog's chest. The dog needs to have a larger portion of its chest covered.