Just double checking - they were 16 and 32 ton forklifts?!?! ( not 1600kg and 3200kg??) Virtually unheard of to hear a forklift training organisation training new operators on forklifts that big....nonetheless like the previous answerer has said, almost every forklift operator has had trouble learning how to judge tilt, the best ways iv'e found is to get the forks flat/"mast vertical" on the floor and /or at eye level when your'e getting a load from the racks....also comes with experience, but by looking at the mast you should also be able to see if its tilted forwards or backwards....very hard to get it perfectly level, but close enough is usually good enough if your'e dealing with wide pallets like euro pallets, loscam and chep pallets (what we use in australia).... the thin export pallets are an absolute pain!!!

Also as much as you'd like to use something to help you leveling the forks, i'd recommend against it to start off with as its best to learn how to do it by eye in my opinion, you won't always be having perfectly flat floors in every loading/unloading scenario so youl'l have to learn to adjust your tilt backwards or forward to get flat forks (if that makes sense lol)

SJB01, you're not alone in having difficulty judging the mast tilt angle, I think every FLT driver has the same problem because it's due to the fact that the driving position does not give any vision of the side of the mast or forks.
In training for smaller CB's I was told to lift the forks to eyelevel as this gives you the best chance of getting anywhere close to levelling the forks. However, it is still very inaccurate, does not work if your not on a perfectly level floor, and anyone who did this at work would be criticised for time wasting. And obviously it doesn't work at all when you have a load on the forks.
The best solution is to have your truck fitted with a mast tilt indicator so you know for sure that the forks are level before you pick up or put down a load.

There are several types available, but the best by far is the SUMOLevel available from SUMOSafe.net. Not only is it the most accurate, allowing you to level the forks to a fraction of a mm along their length, it is also very simple and clear to use.