Why this structure behaves this way
Bull Call Spread is shaped by positive delta and short vega exposure
Net long delta scaled down by the short upper-strike call. Time decay works against the position early on; the short leg's vega mutes the long call's IV sensitivity, keeping net vega modestly negative.
This page uses the catalog’s illustrative default legs so you can compare direction, time, and volatility effects in one place. Edit the assumptions above to test a different starting point.