Phil you are not alone!
When it comes to cutting glass tiles some diamond wheels perform better on some glass tiles but there can be a trial and error in the disc selection. Even expensive wheels can cause splits.
We were sent this
tile
And as you can see the disc was only getting a small way in before the glass split.
They tried numerous wheels. Score-and-Snap. They tried wet wheels and they tried radial cutters.
In the end they found a blade that could do it but not before a lot of experimenting. Perhaps Dave at Trade-Tiler can help you on blade selection.
And now for your extra problem of doing them tricky L cuts! As you can see from above even straight cuts in glass proved troublesome.
So my advise again is to talk to Dave.
We were sent that piece because they had a nightmare DRILLING glass as well so we supplied them with the correct diamond core drills.
Cutting and Drilling Glass can be an expensive nightmare..
But with the right discs and the right drills it can be done.
Best of luck !