I likewise gave my Eagletacs away...for other reasons...otherwise I would just show you. I had two Eagletacs, and they were both shorter than any other protected cell I have. You can find plenty of other examples on this forum, with measurements. I'm not saying it because someone once told me that...I am saying it because i KNOW it, from personal experience.
This page has a list of cells, and lengths. Thanks HKJ! It clearly shows the Eagletac 3400 as shorter than the Keeppower 3400. Other cells, with lower capacity, are even shorter. Your claim that "The KeepPower cells are the shortest cells in a protected button top battery you can purchase" is demonstrably false.
I never said they were flat-tops, and I'm not a newbie here...I am familiar with the difference, and I tried it with button-top unprotected cells - they simply were not long enough. Even your own quote demonstrates my point...Nitecore's own documentation acknowledges that unprotected cells are TOO SHORT to be used in those lights.
And I know the unbranded green cells are iffy...they compress the springs too much, and may make other, shorter cells unusable. Perhaps you got some that were even longer than typical...there are several different versions out there, and the lengths vary. I've amended my earlier post to acknowledge that excessively long cells can be a problem as well.