That's Airbus A380 hangar sized chamber, to me. I have a couple like that but seldom smoke them - 18mm x 25mm is more my thing and I smoke to the last. I also have a couple with narrow chambers but way too deep - I put mesh basket screens in those and they're fine like that.
Big chambers are ok with ribbon cuts, but you better love the blends else boredom can set in.
Most of mine tend to be "standard/average" size at about 18-21 x 30-35 mm (.78-.82 x 1.2-1.4 inches). They all average about 45 min, but can be anywhere from 30 min to 1 hour depending what tobacco and how I am smoking.
To the OP, you can just let the pipe go out halfway (might have to choke it off, just put a pipe cleaner in the stem and cover the bowl, or you can touch a metal tamper to the tobacco without drawing and it'll act like a heat-sink to take away heat and block some air) and then come back and finish it later. That's maybe less ideal than only filling halfway, as
some tobaccos
might taste stale when you return, depending how long it's been.
If your current method of filling works for you, just do that same method but without going as high. If it ends up over-packed, you can turn it over and gently bump it on your palm to loosen, and if it's under-packed, your first few tamps should straighten that out.
The key thing is to not worry and overthink it, it's not rocket surgery.
