This is correct, but since there's a huge difference in hipfire FOV (73.74 vs 120), it might throw the feeling off a bit. Remember that the scopes are matched to the 73.74 FOV of CSGO, not BattleBit's FOV. It might not suite the gameplay of BattleBit as much, but if you set the FOV to 74, everything will be pretty much identical.
The end result for the scopes are exactly the same as when using 26, except for as you say Ironsight witch will be very high. The recommended way is using the values from the "All" conversion as that keeps everything matched.
The reason the more powerful scopes all come out to the same value is simply because of the lack of decimals.