back reflection help please

I am building an 808nm >1W laser into a custom heatsink but would like to keep it under the (coated) glass to make it easier to clean as well as waterproof it.
How much will back reflections kill this kind of diode?
I'd like to try it with a casio 445 as well if there are no issues.
I posted a similar question a while back but only got one response and I don't think it was a veteran.
I'll put it together right now but wait for confirmation before firing it up.

I've done something similar with a 2W diode in a flashlight host.
I first measured the % of reflection from the window. I don't remember what the numbers were, but it was not that much.

I would not worry about it. In my experience, the only time back reflection has been an issue was with reflections from a mirror. Transparent glass surfaces don't reflect enough light back to the diode to cause any damage. Usually its 4-8% total.

By the way, be careful with that laser. IMO, it's not very safe to have an invisible 1W portable laser especially with no safety features (an LED indicator at minimum).

True enough.
It's safe enough for my uses because I use proper safety gear and it will always get its dustcap when not in use. I have had friends over that play with stuff on my kitchen table. So far I have been safe and usually remember to pull the batteries out of my lasers.
I should really start locking the class 4s in the gun safe, I usually have batteries laying around and it isn't much of a stretch that someone might put a battery in when I'm not around.