Pisner beers aren't really typical of Prague, and Staropromen gets a lot of ribbing for their yellow beers over there. Most pubs carry Urquell or Budvar Pilsner, with Staropromen relegated mostly to supermarkets. Not that I'd blame their yeast for that, and it probably could make a fine Pilsner.
Prague, however, is more of a Dunkle town, historically, since it has hard water more like Munich and the OPs than Pilzn. This is probably the yeast used by U Fleku to make their famous Dunkel. I'd use 2782 yeast to make a Dunkel or Schwarzbier,
I am sorry to tell you that you are wrong.
Pilsner style beers are brewed all over the Czech republic and are as native as Hamburgers for good old US of A.
If you could not find Staropramen on your visit there, may be you should have walked off tourist track and find out where and what native are drinking.
U Fleku is a tourist trap and for 60 crowns a pop you will not find too many natives there.
By the way water for Bo - Pils should be from soft to moderate.
You adjust your recipe based on your water.
If you have soft water you can add more hops.
If you have moderate water you use less hops.
You should have NO lingering bitterns regardless of water hardness.
Also Bo - Pils should not be too bitter.
Pilsner Urquell is 34 IBUs.
Hope this help.