Low fuel light

I have a low fuel light on my annunciator panel. the problem I am having, is that it runs off of how many gallons are in the tanks, not percentage.
example: I have it set to on at 20 gals remaining..good for a cessna or mooney, bad for a 737
.
Is there any way I can run it off of percentage remaining? If so, what is the offset? I have looked and cant find it.
PS I am running FSX
Thanx in advance.
example: I have it set to on at 20 gals remaining..good for a cessna or mooney, bad for a 737

Is there any way I can run it off of percentage remaining? If so, what is the offset? I have looked and cant find it.
PS I am running FSX
Thanx in advance.