I have a 2010 LR4 with the RSES.
I had a 2008 RRS with the RSES.
My kids are now 6 and 5 and have not had a problem with viewing angle for them in the 4+ years of ownership and using this system. But my kids are in booster seats (ie kids' car seats) which effectively puts them at the perfect viewing angle.
No, you cannot tilt the screen. But I think anyone over 5 feet would not have a problem viewing the screens and the use of kids seats effectively puts their head at an adult height.
Are you using kids seats? Maybe your kids are too old for kids seats yet maybe too short to view?
Getting a $25 booster seat (see pic) may be your best (only?) solution.
My second guess is that maybe there is an issue with your screens. Looking at mine, I can see the screen through a variety of different head angles.