forget the streamlining
look at the wing/stab/elevator rudder fin-- from a structural point of view
If yo u make the lightest structure which will still be strong enough- you have done your job correctly.
flat , rounded a little , who cares .
It is actually getting structure correct at the lowest weight ,that really counts.

Don't believe this ?
OK
turn back the pages of time -to the first half of the 20th century - look at the evolution of tail groups
Typically the air pressure on the elevator tends to deflect the stabilizer - so take care of twisting loads
bending loads should be obvious if you have some basic engineering.
stabs need to be STIFF-- elevators - not as stiff .