Halitech and Sona, thanks for the hints!
I did a search for butt-stitch and got some nice sources to learn more about it.
Note that I buy the leather completely finished and then just cut it to make the rings.
This is what I'm using for my tests:
http://www.curtidoscarrasco.com/2816-thickbox_default/perfil-de-piel-de-1-5-cm-en-beige.jpg
Sona, yeah it was stitched dry.
I can't find much about preforming in the forum, though I know what it means in principle.
I could actually make some "moulders" and place the rings (not stitched) inside so they would start taking the final shape.
But do you mean I should treat them somehow, place them inside the moulder and let them dry there? Then stitch?
Cutting at a 5 degrees angle might be challenging because the leather is quite thin, about 2 mm, but I get the point and defenitely it should help with the joint if I can get some angle there. I have to play with that.
Also the thread I've used is far to thick, I have to find something better.
Cheers and thanks again.