The controller limit is determining the actual output limit. So if you have a 100W tube that the Ruida has a maximum of 80%, the tube will only output a maximum of 80W (actually it will be more or less, as it’s not perfectly linear).
If you set Lightburn to output a job at 50% in such a situation, it’s outputting 50% of 80%, or 40W.
Manufacturers do this for a few reasons - to improve the longevity of the tube and cut down on warranty claims, or to limit a non-adjustable power supply for the budget manufacturer that’s saved ng a couple of bucks everywhere they can,
In my opinion, it should be set to 100% and the PSU adjusted to give whatever figure the customer wants. In my case with my Reci W4, I cut more than engrave but want a decent lifetime for the tube, too, so I have my PSU outputting 28mA and my controller set to 100%. I could have it set to 30mA and use the 80% rule to allow me to overdrive the tube up to 130W if I need it, but I have a 150W for that, soon to be a 180W and maybe a 300W.
In the first instance, check what power your PSU is outputting compared to the specification of your tube, while you’re there, check that your PSU has a pot adjustment to change the maximum output.