Actually, I found that the system works better if you use 3d12 and a base of 20.

I know, I know, 19 and 20 are just as likely. Why 20? Why not? the effects are the same mathematically regardless of which one I choose.

So far, it looks like given a resolution mechanic of Attribute Score + Skill give you the plus/minus to apply to 20 and assuming a nomral attribute of 3 and a normal skill leve of 2:

A Range of 15 through 25 would denote a success. The chances of acheiving success are a shade over 70%. The built in system of diminishing returns means that a person with a score of 6 and a skill of 6 has only a 90.5% chance of success.

Not bad. Still more to look into

It centers around 4d6. I call it Base14.

Basically, your chance of success is a roll of 14 on 4d6. It is the most common roll, but still something like 11% chance. Your skill bonus gives you lower and higher numbers on either side of 14. For example, if your skill bonus is +5, your range of success is 9 - 19.

I have to double check the percentages to see if this is viable.