refine mesh in volume using stretch factor

Hello

I am new on Trelis. I tested the functionality of the tool and would like to know if it is possible to refine the mesh by using a scaling function and a multiplicative factor.
So the mesh near the walls gradually increase to reach the mesh size of the contiguous volume. Do you know what would be the best method to do this?
In my exemple, I want to refine mesh in volumes 1 and 3 and don’t modify mesh in volume 2.

brick x 10 y 10 z 1
webcut volume 1 with plane xplane offset 4.5 noimprint nomerge
webcut volume 2 with plane xplane offset -4.5 noimprint nomerge
undo group begin
imprint volume all
merge volume all
undo group end
curve 18 interval 5
curve 18 scheme equal
curve 36 interval 50
curve 36 scheme equal
curve 41 interval 5
curve 41 scheme equal
curve 1 interval 60
curve 1 scheme equal
curve 12 interval 1
curve 12 scheme equal
surface 21 scheme map
mesh surface 21
surface 8 scheme map
curve 17 interval 5
curve 17 scheme equal
curve 17 interval 5
curve 17 scheme equal
mesh curve 17
curve 18 interval 5
curve 18 scheme equal
mesh curve 18
surface 8 scheme map
curve 1 interval 23
curve 1 scheme equal
curve 1 interval 23
curve 1 scheme equal
mesh curve 1
surface 8 scheme map
mesh surface 8
surface 23 scheme map
mesh surface 23
surface 24 20 11 scheme map
mesh surface 24 20 11
surface 6 scheme map
mesh surface 6
surface 18 9 26 scheme map
mesh surface 18 9 26
surface 19 10 25 scheme map
mesh surface 19 10 25
volume all scheme map
mesh volume all

Hi,
I tried the stretch factor function but the result does not satisfy me.
Curve Scheme Stretch [First_size ] [Last_size ] [Start Vertex ]
I got what I wanted with Option “bias” and “intervals count”.
Curve Scheme Bias {Factor|First_Delta|Fraction} [Start Vertex ] [preview]
what is the difference between the two options?
thanks a lot