Header Logo Problem (Ignoring Custom Size CSS / Fixed Width)

I have turned on the resize option in General > Branding
and I choose the Resize Method to Fixed Width with 124 Logo Width and 40 Logo Height
Screenshot: https://prnt.sc/lv7lu7

But that setting just won’t work, AMP for WP just ignored my setting and use the default setting 190×36 which is really terrible.
Screenshot: http://prntscr.com/lv7ly3

So, I tried to use custom CSS to make the header logo width more relevant.
Screenshot: https://prnt.sc/lv8y1t
But the custom CSS is useless and doesn’t make any change to the logo size.

After I search trough AMP for WP WordPress Support Forum, I found one thread that having same trouble as I faced, (https://ww.wp.xz.cn/support/topic/amp-ignoring-custom-logo-image-size/) and @ahmedkaludi suggesting to use Flexible Width instead Fixed Width, that solution seems worked for this kind of problem, so I want to try that option too, but when I switch to Flexible Width option, this is what I get: http://prntscr.com/lv7mvb.

The slider on Flexible Width option is not available on my dashboard, which is very annoying.

I’ve tried to disable all my plugin except AMP For WP and hope the slider is gone because I assume there is a conflict between my plugin with AMP For WP, but that is just won’t work.