Of the three things you noted - strength of ligs, strength of BC, and the position of the internal penis - I don’t recall that Bigger was ultimately concerned with any of them when he proposed the LOT Theory.
For example. Someone with an inner penis that points straight forward, who has tight ligs, and who has a weak BC, might be able to see tugback at eight. Mainly this is because his inner penis angle is low and his tugger is still nearly “in line” with his outer penis. Another guy who also has tight ligs, has an inner penis that points up, but who has a strong BC muscle, might also have a LOT of eight. Why? Because his tugger is so strong it can pull things “around the corner” as it were. Neither has “loose” ligs. My problem with the theory is that it was not taken to the needed depth anatomically before it was released on the public.
Bigger was concerned with gauging the length and position of one’s ligaments and how knowledge of that could benefit a PE’ers approach to expediting length gains.
How many men really have “loose” ligs anyway? Why do we have the suspensory and fundiform ligaments? To hold the penis, while erect, at the proper angle to enter the vagina (suspensory) and to keep it centered during intercourse (fundiform). A better way to tell if your ligs are loose is if you’re having difficulty keeping your penis pointed in the right direction during sex. Loose ligaments are not normal. I sincerely doubt that anyone with a low LOT has authentic loose ligaments. It’s more likely that they have a low angle inner penis, a strong BC muscle, or both.