It seems to me that there are fairly large individual differences even within
one species with regard to ideal growing conditions. My N. ventricosa
produced fist size pitchers outside here in Florida with 4+ hours of direct
sunlight, but did not over winter well when the temps were down typically into
the 60-70s F. Winter humidity dropped too, of course, but was still typically
in the 70+% range.
As for the production of upper pitchers, seems to me that some species
simply don't produce upper pitchers as well as others. N. ampullaria,
as I recall, does not. FWIW, I have a N. amp x anamensis cross which
doesn't seem to want to produce upper pitchers either. After it gets
about eight inches of growth, a new basal shoot becomes active and
begins to grow, it gets about eight inches and then another becomes
active, etc. N. x hookerianna (amp x raff) on the other hand produces
distinct and attractive lower and upper pitchers.
As per flowers, I have a whitteii x thorelii cross about 8 inches high
that has already bloomed. Only lower pitchers so far. In my very
limited experience the Neps continue to grow but stop producing pitchers
when they begin to bloom.
Tom in Florida