Tempering glass just makes it resistant to shattering it doesn't allow for more light transmission. Your glasses are tinting because of the uvA ,the glass allows a good portion of that through,however UVB is what's been proven to increase thc content.
http://wiki.cancer.org.au/policy/Position_statement_-_Tinted_windows
UVA is still good for bringing out the anthocyanins aka purple but uvb is the hard one to come by and the tempered glass blocks it all. Standard mh are great for UV supplementation crushing the cmh in terms of output..... UVA and B
I touched on this in an earlier post. First law of thermodynamics: energy cannot be created or destroyed. When you raise your lights your photons are just spreading out according to inverse square law they're all still there until they hit something that isn't 100% reflective they just keep bouncing around losing energy each bounce depending on the pigment/material they're bouncing off of. They hit something flat black and it mostly all gets converted to heat. And the closer you bring your light the smaller your footprint is so you lose space you could have more or wider plants. Plus your plants can only use/tolerate so much light intensity before the enzymatic wheel that drives photosynthesis just slips or your plant gets fried.
When I ran ac hoods I could put my hand on the glass in the winter time so I thought I could keep my lights really close but it just fried my plants and melted trichs. AC hood guys always bring that up but it really is a moot point.
In the case of multiple light sources running them higher will also give you more overlap ,less shade angles and more penetration......If I'm wrong, show me some info saying otherwise- I take no offense to being corrected I'm all about learning