Hi, I see your 444 is painted yellow which could indicate that it is an industrial model 2444. Does it have a hydraulic pump in front of the rad connected to the crankshaft? Or only the regular hydraulic pump on the right side of the Diesel engine?
If it has only one or two pumps on the right side of the engine then there is a shelf like structure that you can see looking through the filler hole and the correct fluid level is when the shelf is covered with the tractor sitting level.
Hopefully if you take that top pipe plug out and open the valve and with a light you can see the shelf in the reservoir otherwise you will have to remove more the return piping. We had a 434 and 384 (same tractor) with 1550 FEL and only one pipe T and plug and you could see the shelf by removing the plug.