Is there a strategy in preamp tube placement?

     I couldn't agree more, that a tube buyer should be familiar with their seller.   BUT: that's seldom the case, with the first-timer or neophyte.

"...but there are many among us who don't know what you are talking about when you use terms like "bottom gettering, a very unique top mica and support structure, including copper posts*"."

     Perhaps: that would explain the existence of this website, it's educators and an Internet, replete with pictures and vids*, to instruct/guide such, in their pursuit of the hobby and better sound.

                                            *ie: see above

         Of course: CAVEAT EMPTOR will always remain a prime directive!

                                          Happy listening!

     btw: Crazy price on that linked, eBay pair of KRs (to me, anyway), BUT, then there’s:

https://www.ebay.com/itm/174924762007?hash=item28ba540b97:g:1UYAAOSwfj1hNNVb  (PLUS SHIPPING!)

     That French seller is clearly very proud of his tubes!

"These days I’d also be leery of counterfeits of tubes that are now 70 and more years old.

The best sounding KRs are the black glass variant. You can’t see what you’re buying."

     The 1940s, Ken-Rad, VT-231/JAN-CKR/6SN7GT has bottom gettering, a very unique top mica and support structure, including copper posts*, which are plainly visible (blacked glass or not).

     I’ve never seen a counterfeit CKR proffered, though: I’m certain I’ve not seen everything for sale out there.

        On the page linked previously; Brent has a three part vid, on spotting genuine NOS tubes, worth viewing by any seeker.

   *ie: https://www.ebay.com/itm/185479311423?hash=item2b2f6db03f:g:6~QAAOSwGRliuJhB

     YEP (Brent charges $5/tube for noise testing)!

     A vid, describing his testing method, can be found just into the the tube description portion of this page:                       

                     http://www.audiotubes.com/6sn7.htm