Let’s talk about bonuses and penalties to ability scores in D&D and D&D-like games. The whole mechanic of a static penalty or bonus has never seemed ideal to me. In my mind, these adjustments should serve one purpose: to bring a character closer to what you would expect from a member of that species or whatever. But a static adjustment, say +2, doesn’t always do that. Example: you’ve got a half-giant, and you put a raw 18 into their Strength. As far as I can tell, their STR already reflects that they’re a half-giant. No need for adjustment. A +2, +3, +4, or whatever doesn’t bring them closer to what you’d expect from a half-giant. And if they put something really low in there, even with whatever bonus it might be hard to imagine even the weakest half-giant being that weak.
I say a better solution (and what I’m doing in my Dark Sun homebrew) is to set a minimum that if not met, the score increases up to that point. And if it’s above that then you’re good, no change. This helps level out characters, puts a damper on min-maxing and spiking an ability score to a silly place, and it lets you feel a little more like a member of that species. It also serves the “bounded” philosophy of bonuses in 5th edition. For example in my current playtest ruleset, as a dwarf if your Constitution is not at least 15, it becomes 15.
This brings up an issue. Where do you set these values if you want to make an easy conversion right now? The intuition might be to figure the average (10-11), add the normal bonus and that’s the new minimum. That doesn’t feel right to me. I think the reason it doesn’t feel right is because if someone’s playing a species that has a really high bonus in a stat, they’re likely going to be putting a decent score into it. Not a 10 or 11. I say, set the score to whatever has a modifier equal to that original bonus.
So a +2 CON becomes 14-15 CON, a +1 becomes a 12-13, and so on. I personally really prefer those edge scores the best, because it feels more rewarding to be able to bump that up next time you get an increase. The exception I’d say is 18. If a species gives a +4, just set it at 18 if they don’t already have at least 18 in it. This might seem really powerful, and it probably is. At least for what I’m working on it feels right since everyone in Athas is supposed to be more evolved seeing as they’re on a death world. In any case, it’s a fun concept to play with. I’ll write more on it as I see how it plays at the table.