doctorbadwolf
Heretic of The Seventh Circle
None of that is “straightforward” in the sense of being obvious or “clearly the right way to go”.If Strength determines how far you can jump, it seems straightforward to me that it would be easy to jump an additional 5 ft., hard to jump an additional 10 ft., and nearly impossible to jump an additional 15 ft.
A 10th-level character with Strength 10 who has applied Expertise to their proficiency in the Athletics skill can succeed at a 15 ft. long jump if the d20 roll for their check is anything higher than a 1.
The same character with Strength 15 automatically succeeds at a 20 ft. long jump.