When a fixture is added to the strobe group, using the strobe button shortcut does put the strobe speed and intensity to the max value.
Maybe your fixture do not have an intensity channel? In this case you can use the virtual dimmer function.
Maybe you are using an old version of cuelux, where the intensity was not linked to the strobe button.
Current version is 1.6.6.
I hope this will help you,
Enjoy