xrandr with Fractional Scaling to set a percentage value to each monitor (without affect each other)

I use VirtualBox, the Host is Windows 10 and the Guest is Ubuntu Desktop 20.04. The laptop is connected with a secondary monitor of 22 inches (Samsung). I use the following with xrandr

# cvt 3480 2160
# 3480x2160 59.99 Hz (CVT) hsync: 134.20 kHz; pclk: 645.25 MHz
Modeline "3480x2160_60.00"  645.25  3480 3768 4144 4808  2160 2163 2173 2237 -hsync +vsync

xrandr --newmode "3480x2160_60.00"  645.25  3480 3768 4144 4808  2160 2163 2173 2237 -hsync +vsync
xrandr --addmode Virtual1 "3480x2160_60.00"
xrandr --output Virtual1 --mode "3480x2160_60.00" --pos 0x0

# cvt 1920 1080
# 1920x1080 59.96 Hz (CVT 2.07M9) hsync: 67.16 kHz; pclk: 173.00 MHz
Modeline "1920x1080_60.00"  173.00  1920 2048 2248 2576  1080 1083 1088 1120 -hsync +vsync

xrandr --newmode "1920x1080_60.00"  173.00  1920 2048 2248 2576  1080 1083 1088 1120 -hsync +vsync
xrandr --addmode Virtual2 "1920x1080_60.00" 
xrandr --output Virtual2 --mode "1920x1080_60.00" --pos 3480x0

The 2 monitors are configured. The secondary (Samsung) is well applied about size and font. The problem is the primary monitor (of the laptop itself) it is very small and the font is small.

Note: the current settings shown above for the Virtual1 (primary) if is applied when the secondary monitor is not enabled it works fine. So when Virtual2 (secondary) is enabled arises the situation/problem indicated

If I arrive to:

Show Applications -> Settings -> Display -> Fractional Scaling

If Fractional Scaling is enabled and is used either 150% or 200% - just one of them - the primary monitor fits perfect about size and font, but sadly it affects the secondary (a terrible change of presentation). Therefore through Settings - Display both monitors are affected if Fractional Scaling is enabled and set some value.

Question 1 How accomplish the goal to apply Fractional Scaling for each monitor with the xrandr command? but without affect each other? - With what parameter?

Something like:

xrandr --output Virtual1 --mode "3480x2160_60.00" --pos 0x0    --??? 200%
xrandr --output Virtual2 --mode "1920x1080_60.00" --pos 3480x0 --??? 100%

I did do a research about the --scale parameter and I used --scale 2x2 (just how testing)

xrandr --output Virtual1 --mode "3480x2160_60.00" --pos 0x0 --scale 2x2

But it does not work.

Question 2

Is there an official table about equivalences about axb and x%?