Don't know if they are all the same but for me I downloaded the manual for my table and it tells you what angle to set it up at. Just remember to put your level on the play field and not on the glass. Good luck
Machines are not all the same, the manual will tell you the recommended angle for most games.
You are free however to completely ignore the manual and set it up how you like it. Over the years I have got better at playing pinball and I find it far more enjoyable to have the game set up at a steep angle, so that it plays much faster.
You can really alter the way that a game plays just by changing the angle a few degrees, so I would really just recommend having a mess around with the angle till it plays how you like it.
Many games will specify between 5 and 7 degrees, but I prefer 7 - 15 degrees depending on the game
I asked a Deith Leisure salesman about a traded-in Escape From the Lost World many years ago. The problem was its special set of legs (to suit the odd cabinet) had mistakenly been despatched to Turkey with a Radical, leaving the Escape more than a little 'flat'. The Radical must have been just that, though.