C02 laser gets weaker above 50%

My 40-50W co2 laser cuts 1/4" plywood and acrylic well at 50% but above 50%, the cuts get shallower as I increase the power. The current stays approximately proportional to the power setting, but the beam seems to get weeker. Is this normal or a sign of a partucular failure?

The tube has less than 100 cutting hours, mostly at about 45%. I almost never run above 15mA current.

The tube is a TONGLI 40-50W Co2 Laser Tube
35-50W CO2 MYJG Serise Power Supply MYJG-40 OG 110/220V × 1

According to your description, you are not sure whether it is caused by the laser tube or the power supply. It needs to be investigated. Do you have other power sources now?

I do not have another power supply.