The menu should be identical in size to the original Windows 10 one.
The setting you are changing is probably not the one you want as that's more for making things bigger hence the tiny adjustment for being smaller. If the menu is too big then resize it as you did in Windows 10 by resizing it from the edges when you get the resize cursor.
You may also want to set the all apps list to not be always visible in the same way you could on Windows 10. This can be done from the settings page accessed from the start11 settings window via the button at the bottom.
You can set the background to less solid but there is a limit and the blur exists for a good reason. You would find the menu unusable if what is under it could be light or dark. Text could be effectively invisible and likewise some icons could be hard to see.
We do allow the blur to be removed on the taskbar as what is under that is consistent.
We also offer other menu styles which are adjustable in size so there should be a combination you find works for you.
I have no blur on StartAllBack and set the transparency to a point of readability and visible background. So "the blur exists for a good reason" is not true as the menu is very much usable. It's a matter of how you set it up.
The resizing you mentioned is not really accurate... Before upgrading to Windows 11, my start menu had the app list always visible and with Extra Tiles enabled. Start11 claims more of the screen than it did. Some of the things Start11 lacks is similar to how Windows 7 and 10 did: reducing the number of links and applications visible by default. This reduced menu height. The height alone being reduced makes a big difference.
Even though you "do offer other menu styles", if you take the Windows 7 look as an example, customization is not as accessible as StartAllBack.
StartAllBack Example or readable without blur
By the looks of the other replies, Neil, this sort of thing is possible to have added as a feature:
As far as the blur, there is not a way to remove that, although I agree that would be a great option.