You can use an adjustable gas block to adjust the angle that the rifle ejects the casings. You could switch to a LH upper. You could get a brass catcher. You could get a larger brass deflector.
I use a Caldwell brass catcher which has a pic rail adapter on a handful of my ARs.
They're pretty convenient and I like to use mine as often as possible. I don't use them during classes since I've already broken two when moving near/around obstacles.
As far as heat, mine has had no issues with it. There were several occasions where I filled it up pretty quick and then proceeded to burn myself on the spent brass when emptying it.
Lefty here too. My one AR that I just cant get to eject 2-4:00 I gave up and put a brass catcher on. Messed around with weights adj gas the whole bit. Could never get it "right"
https://www.amazon.com/Caldwell-Resistant-Convenient-Picatinny-Collection/dp/B00EB5OU0Q?th=1
For pistol, when I'm testing loads indoors I bench rest it, seems to help to keep the brass in the same place. For AR’s I use this: https://www.amazon.com/Caldwell-Resistant-Convenient-Picatinny-Collection/dp/B00EB5OU0Q You can buy additional pic rail attachments for every gun, so you only need the one basket. I use it every time I shoot now.
Shell catchers are almost universal, Spring Thunder shells are a lot bigger than Firefly shells so the shell catcher I'm using (or any shell catcher for that matter) should work for the Firefly since it also has rails on top. Here is the one I bought: Amazon
Edit: whoops, wrong link before, fixed!
Is your AR a slab side? I shoot left handed and everything but one shotgun is right handed. I have never been hit in the face with brass. One .22 rifle I have will get me with some dirt and crap but that's it.
I do use a brass catcher on my AR, because I am lazy. I use the Caldwell that attaches to the rail. It works good and stays out of my way.
https://www.amazon.com/dp/B00EB5OU0Q/ref=cm_sw_r_cp_apa_glt_fabc_YGHASKDCNPYPQK6EA756
This would probably be better for shot shells.
From Uncle Jeff no doubt…
https://www.amazon.com/Caldwell-Resistant-Convenient-Picatinny-Collection/dp/B00EB5OU0Q
Depends what shotgun you have if it has a PIC rail this one will work https://www.amazon.co.uk/Caldwell-Outdoor-Catcher-available-Bronze/dp/B00EB5OU0Q/ref=pd_sbs_200_1/258-4704576-4322424?_encoding=UTF8&pd_rd_i=B00EB5OU0Q&pd_rd_r=9c358ed6-ba48-4bc1-b7ee-c1852684311c&pd_rd_w=tOqTl&pd_rd_wg=SStcb&pf_rd_p=2304238d-df78-4b25-a9a0-b27dc7bd722e&pf_rd_r=VT849XP10YNM2PDSWQJR&psc=1&refRID=VT849XP10YNM2PDSWQJR if not then something like htis might be usable https://www.amazon.co.uk/UTG-Deluxe-Mesh-Shell-Catcher/dp/B001VIJLAU/ref=sr_1_3?dchild=1&keywords=shell+catcher&qid=1605521755&s=sports&sr=1-3
This is kind of the opposite of what you're asking for, but I recommend that you avoid this Caldwell brass catcher. I tried using it with my AR once, and it quickly became apparent that it wasn't worth the effort to save my (.223) brass. I could barely get through a mag without the bag sagging or spilling/deflecting hot brass onto my hand and needing to be adjusted or emptied out. The price might be tempting, but the velcro and wire frame just don't provide enough support for the bag once it gets close to being full.
On the other hand, this model seems to be sturdier and more thoughtfully designed, and also has a significantly higher capacity (approximately 100 rounds, instead of the roughly 30-round capacity of the brass catcher I mentioned earlier). While I haven't decided to pick one up, you might want to look into that model if you'd like to save your brass.
https://www.amazon.com/Caldwell-Pic-Rail-Brass-Catcher/dp/B00EB5OU0Q they have one that might work, looks like the adapter connects via the pic rail then the catcher connects to that.
Works great. Stays put, catches shells, easy on and off. This model. Inexpensive too.
Maybe get a pic rail brass catcher like this one. If you leave the zipper open, the brass will just drop on the ground right in front of you.
they use devices to catch the brass as to not leave evidence. sometimes just wrap it up in a plastic bag. at least that's what i've seen on "the first 48".
https://www.amazon.com/Caldwell-Pic-Rail-Brass-Catcher/dp/B00EB5OU0Q
This brass catcher is pretty awesome.