Why do wmaker icons shrink?

Why do wmaker icons shrink?

I find myself spending too much time getting the wmakers icons right. When
I start an application from the commandline I get an Icon, which I can
attach to the dock or the clip. Good.
However, when the application is not running, the icon shrinks to about
half the size. The tile keeps its original size (48x48) but the image in
it gets smaller. This small image does not look good.
I can work around this, by explicitly specifying an icon (rightClick ->
settings). But it just takes too much time to browse through all the
available icons (unless there is a fast way I am not aware of). I would be
happy if wmaker just kept the icon it originally displayed.
Seems like I do not fully understand, how wmaker can display an icon of a
running application just fine, but sometimes requires configuration, when
the application is not running.
So why do wmaker icons shrink and what can be done to avoid spending too
much time in getting the icons right?