I'm not a sniper,and I do not practice shooting glass...
I did read John Plaster's book "The Ultimate Sniper"
He addresses the topic.
A military sniper has a different goal than a police sniper.
The police sniper typically counter sniper or preventing the death of a hostage.
Scenario,Bad guy holding his ex-wife waitress inside a restaurant,probably bent on murder/suicide or kidnapping.He has an arm around her neck and gun to her head.
He's hot,flipping out.Probably going to kill her.
The shot through glass is uncertain.
If the bad guy is not CNS disabled,he can/will shoot her.
What do you do?Do nothing,she dies.Do something,she still may die.
Whatever gives her the best chance to survive,and the odds aren't all that good.
Perpendicular to the glass is best.Doubleteam snipers is best,one breaks glass,the other bullet connects.
One thing I was surprised by:The direction of deflection was the opposite I would expect.I would intuitively assume a deflection similar to skipping stones off water or a typical ricochet off the ground.
Not so .
If the sniper is shooting down through the glass from above,the bullet will be deflected up.
Several years ago,that restaurant scenario occurred in a Northern Colorado town.
At that time,this was 20,maybe 30 yrs ago,PD training in general had not caught up these scenarios in this town.
The police rifle was a .243.Great for some scenarios,maybe not for shooting through glass.
In any case,the effort failed.The woman was killed.
A restaurant customer,who was in the rest room,attempted to escape the rest room window.
Unfortunately,he died from multiple hits of police 9 mm.
Easy to armchair,but testimony that the OP's question is a good one.
Had more prep/training taken place,maybe ,but only maybe,the results could have been better.
Hindsight.