You may be over thinking your chances of "falling out" of the JX3, not that it is impossible, but highly improbable.
The JX3 is probably the safest saddle as far as falling out of it, due the rigid bottom and back, waist belt, leg straps and shoulder straps.
It is very "self balancing" , there is a horizontal strap with clips, to keep the shoulder straps in place, even when the shoulder straps are loose.
If the JX3 is your first saddle, you may need to fine tune your strap lengths.
The JX3 is probably the safest saddle as far as falling out of it, due the rigid bottom and back, waist belt, leg straps and shoulder straps.
It is very "self balancing" , there is a horizontal strap with clips, to keep the shoulder straps in place, even when the shoulder straps are loose.
If the JX3 is your first saddle, you may need to fine tune your strap lengths.