I just got a T-Bird Studio 5, and I HATE the way it hangs on the strap.
No tummy cut on these, but set-neck rather than neck-thru, and a smaller headstock. They don't neck dive anywhere near as much as the neck-thru versions do. Previous owner had fitted Dunlop Straploks, which I like, but the strap button at the neck heel is not workable for me.
The straplok on the neck heel makes the bass angle out away from my body and the extra turning moment makes the bass tend to lean forward, bass bout toward the ground. My 'Bird is flipping out!
So I moved the strap button to the upper horn. Heresy. Madness. Insanity. But it works for me.
In my defense, both Mike Lull and Spector have sold nice (very nice) Thunderbird-shaped basses with strap buttons on the horn. Interestingly, the photos on the Spector site of the Rex and Rex 5 show the button at the neck heel, but the one that Rex is actually playing has its button on the horn.
On my Epi T-Bird, the strap button on the horn makes the neck fall down. Real bad. The strap button on the neck plate is much better balanced but the bass still flips forward. Tough call as to which is worse.
The damage has been done, I put an extra hole in my bass. It was either that or sell it on the Classifieds

But at least it's a black bass and it'll be easy to touch up later if I sell it.