Some basses are just tighter than others. This can be from a combination of string length, design overall, neck pitch, neck stand, bridge height, tailpiece material or tail wire length or whatever.
I have personally owned and played on dozens of basses. I totally except the fact that some are looser and some are tighter. I just set each bass up tweaking it to where I like it and then just play it. For instance, my Martini is slightly looser than my Hart. Big deal. In about two minutes of playing either bass, all is forgotten.
I prefer my soundpost set for the darker sound on each bass. Try what Arnold said and see if a 'Post position change gets your bass to where you like it. I think for the most part basses vary quite a bit in tension due to all the above mentioned and in combination of them. Set the bass to where it feels best and go from there. On a new bass you can sometimes see huge changes from season to season as just a slight swell from humidity approaching the summer months or a contraction in the wood as the fall season starts the bass is adjusting itself for the months to come. Get used to this. It's life with a carved bass..
