Bottom ribs touch pelvis bone (poor mobility/posture)

Hi, I wonder if anyone can help.
I'm a male in his 30s with no formal medical diagnosis (I've seen an neurologist and had Mris of the spine which were OK).

Basically, I've realised my lowest ribs are almost touching the top of the pelvic bone around both sides and the back (i.e. the ends of the 11th and 12th ribs almost touch the top of the iliac crests - around 1/2 cm gap). There's no pain but a lot of tightness and poor overall mobility and this effects posture. Also I have muscle weakness in the back, abdomen and buttocks with some kind of spasms. This has been going on for several years.

Is it unusual for the ribs to be so low down and close to the pelvic bone? The skeletal diagrams I've seen show a significant space in there.

In terms of self-help, I do stretches, resistance bands and use a foam roller. I work on the whole body but focus of SI joint exercises. Has anyone experienced this or come across this before?

Thanks for any thoughts or advice