I think that’s pretty much it…
When you generate a gray scale and it loads into the Ruida, you can see the vast increase in data sent to the machine…
We can’t figure out the simple part, I’m not going there yet… 
I was burning a line, so I would not expect the L signal to change. It does change if you look at the first photo…
Good night…
The above is why I suggested you try syncing on the laser current and looking at the PWM.
The L-on may be an enable at the start of the job, line, or who knows what. The start of firing may or may not be the L-on? So you may see traces where the PWM and L-on are out of sync. It depends on when the scope happens to trigger amongst a gaggle of scans.
In an original* K40 and controller, the image is dithered and therefore the beam is turned on and off with the L signal for each pixel position. There is no grey shade. [this is what I was told].
Smoothie controllers only turn on the PWM signal when needed [which is a composite of L-on and PWM] this is why an additional “enable” is not needed and the IN can be used as a power adjustment.
Keep in mind that aside from how it is used IN is really an analog input and L is expecting a solid ground. Neither circuits are actually a digital signal in the classic sense.
Oh, and BTW if in a Rudia machine the PWM and L-on are synced changing it to a pot and L may not work.
During my ‘sleep thinking’ last night I hit upon the idea of logically ANDing the two Ruidia output controls to get a functioning output for LPS-IN control.