I guys, my name is Chris (i speak little english) and today i would like to talk about 2 preflop situations:
1) Hero is BB and Villain SB
2) Hero is SB and Villain is BB

1) We can talk more and at least optimal defense frequency but we know that we can increase the defense, the question is how much?

I calculated considering sb fold:
if villain Open 55% from sb with size 3x
2.5/4= 0.625 odf%(1-fe%)= 0.375 = play with 37.5% of range
but When he fold he lost a sb!!!
considerino this :
0.55 ( 1.5f - 2.5*c) - 0.45 ( 0.50 ) = 0
0.825f - 1.375c = 0.225
C = 1 - f
0.825f - 1.375(1-f) = 0.225
0.825f - 1.375 + 1.375f = 0.225
0.825f + 1.375f = 0.225 + 1.375
2.2f = 1.6
f= 1.6/2.2= 0.72
72%

I think it is good to know the minimum defense but our problem is how can we defend?
example: Villain opens Sb 2.5x or 3x with a range of 45-55%.
I have to take into account a factor R?

2) In this particular situation I am wrong.
I think I can have my open sb> open btn as defense is the responsibility only on one player.
Often in my level NL50 people fold about 60%..With size 2x to 3x my fe% goes from 50% to 62.5% could almost open atc but problems arrive when villains 3bet me.

thx to all for help me :)