I'm a 41 Long Suit Size Medium Frame

Executive Summary: Unfortunately, after much trial and error, I can confirm that no undershirt fits perfect.  The best you're going to get is the Jos Banks size Large followed by Dockers size Extra Large.  These shirts are higher quality material than the standard Hanes and have a nice length to tuck them in even after shrinking from washing.

Hanes Size Large (The kind you can buy at your local big box store)
<a data-hook="product-link-linked" class="a-link-normal" href="/Hanes-Comfort-Soft-Crew-Neck-5-Pack-Tee/dp/B005SN5HNY/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">Hanes Comfort Soft Crew Neck 5 Pack Tee</a>
Prior to Wash Length: Nice tuckable length
Prior to Wash Fit: Baggy
After Wash Length: They shrank up the most of any shirt.  They really aren't even tuckable now.
After Wash Fit: Still baggy
Quality:  These are the thinnest of all the shirts reviewed here.  The thin material, the bagginess and not being able to tuck them in, let alone keep them tucked in, is the reason I decided to try all the shirts below in search of a nicer quality better fitting shirt.

Hanes Size Large Tall
<a data-hook="product-link-linked" class="a-link-normal" href="/Hanes-Mens-Classics-Tall-Man-Crew-Neck-T-Shirt-9856/dp/B000KBCQTC/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">Hanes Mens Classics Tall Man Crew Neck T-Shirt # 9856</a>
Prior to Wash Length: They were as long as the Dockers Extra Large
Prior to Wash Fit: Baggy.  Half an inch wider on each side of the shoulder than the Dockers Large.
After Wash Length: Nice tuckable length.  A tad shorter than the Dockers Extra Large
After Wash Fit: Tight through the shoulders though just slightly looser than the Dockers Large.  They dug into my arm pits a bit.  Slightly uncomfortable.
Quality: They are thick shirts, almost as thick as a standard t shirt (non-undershirt).  2 or 3 times as thick as the standard Hanes undershirts and thicker than all other shirts mentioned here.  For this reason I don't like them.

Adidas Size Large
<a data-hook="product-link-linked" class="a-link-normal" href="/adidas-Men-s-Athletic-Comfort-Climalite-2-Pack-Crew-Undershirt/dp/B004RKJ3E8/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">adidas Men's Athletic Comfort Climalite 2-Pack Crew Undershirt</a>
Prior to Wash Length: Reasonable tuckable length
Prior to Wash Fit: Tight all around
After Wash Length: Barely tuckable
After Wash Fit: Almost as tight as a compression shirt.  Tightest of all the shirts.  They dug right into my arm pits.  Uncomfortable.
Quality: The material is nicer and a tad thicker than the standard Hanes you can buy locally.  Way too tight to wear.

Dockers Size Large
<a data-hook="product-link-linked" class="a-link-normal" href="/Dockers-Men-s-4-Pack-Crew-Neck-T-Shirt/dp/B001O9BEEM/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">Dockers Men's 4 Pack Crew Neck T-Shirt</a>
Prior to Wash: Nice tuckable length
Prior to Wash Fit: Comfortably loose, not really baggy
After Wash Length: Still tuckable, but they did shrink quite a bit
After Wash Fit: Tight all around, but not as tight as the Adidas.  They dug into my arm pits.  Uncomfortable.
Quality:  Nice material, not too light like store bought Hanes, not too heavy like the Hanes Tall, but Jos Banks is just slightly nice, especially the collar.
Note: I bought a second package to confirm that I didn't receive a bad batch that overly shrank.  Unfortunately the second package shrank just as much.

Dockers Size Extra Large
<a data-hook="product-link-linked" class="a-link-normal" href="/Dockers-Men-s-4-Pack-Crew-Neck-T-Shirt/dp/B001O9BEEM/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">Dockers Men's 4 Pack Crew Neck T-Shirt</a>
Prior to Wash Length: A bit longer than the Dockers size large
Prior to Wash Fit: Baggy. About 2 inches wider on each side of the shoulder than Dockers size Large
After Wash Length: Nice tuckable length
After Wash Fit: Baggy.  They shrank up width wise so that they are about 1 inch wider than the Dockers size Large
Quality: Same as the Dockers size Large
Note: They are a tad too big for me, but I'd rather have that than too small.

Jos Banks Size Large
Not sure if these shirts show up in the Product Ads from External Websites, but they should if Amazon really wants to compete against the best, which is what this section of the website implies
Prior to Wash Length: Slightly longer than Dockers size large
Prior to Wash Fit: Baggy
After Wash Length: The length barely shrank at all.  They are about 3 inches longer than the Dockers size Large after washing
After Wash Fit: Slightly baggy.  Between the fit of the Dockers Extra Large and Dockers Large.
Quality: The material is a tad nicer than the Dockers, especially the neck.  Time will tell, but I imagine the neck would be the last to roll out of all the shirts I've tried.
Note: I found these on sale for about the same price as the Dockers