Hello there Lefty,
Last year I faced pretty much the same challenge with a bike I purchased from my favorite LBS and perhaps the fix that worked for me might work for you. I just took a photo as well to show you and hopefully it helps out.
I'm 6'0, currently 270lbs and a 32" inseam and 34" sleeve. My weight was 305lbs at the time of purchase last year and worth noting when you see my seat setup.
My LBS had a Medium and Large frame Giant Toughroad in stock and was the perfect bike for me to transfer my not-being-used rear hub motor setup from another bike onto.
I tried out both the Large and Medium (yes Medium) frame sizes on his Fit testing setup.
Everything about the Medium frame was perfect fit for me except my long torso and just like you - I needed the seat to go back 1-2 more inches.
The solution? I upgraded to the Selle SMP AVANT seat under his guidance (had it in stock and ready to install). A bit pricy yes ($320 Cdn last summer) but it's an amazing seat and because of it's exceptionally long bars it was able to give me the 1.5" I needed for a perfect Fit.
First, here's the seat link:
Wide and well-padded model that the ladies really love! Recommended for pants sizes: LXLXXL
www.sellesmp.com
And as mentioned, here is a photo I just took to show you the seat position I am riding on my Medium frame bike:
I thought to add the tape measure to really capture the length this seat can be adjusted.
I have since put on over 1,500kms on this setup and I'm 100lbs your senior - without any issues. Granted the D-Post of the Giant Toughroads is amazing and takes my size and weight well, which is the last point I will suggest keeping in mind if you swap to a seat that goes farther out the back.
Another bike I have (but not handy) was a medium frame I picked up used and had the same cockpit issues. I put a SMP Selle AVANT on it and noting the original seat post was already starting to bend under my weight - upgraded to a Thompson seat post. They are rated for up to 400lb riders and last forever. Here's a link to them if you feel you might need a stronger seat post for the seat solution you decide to go with:
Shop our selection of premium seatposts, ideal for customizing your ride. From elite designs to covert droppers, ensure optimal fit and performance.
www.bikethomson.com
Final note - what I learned last year and share with you is with a little bit of budget you can upgrade to a seat like I have shown that gives you the adjusting length you need and a stronger post if needed (but at 165lbs you should be fine) to make the 'Fit' of your bike perfect for you.
Good luck!
