Don't forget that the blinds have dead money in front of them which means they face better pot odds on a call than other positions.

E.g. Someone opens 3x.
Everyone between him and the blinds has to call 3BB into a pot of 4.5BB. They need at least 40% total equity to continue with a call.

The SB has to call 2.5BB into a pot of 4.5BB. He needs at least 36% total equity to continue with a call.

The BB has to call 2BB into a pot of 4.5BB. He needs at least 31% total equity to continue with a call.

What Keith said is absolutely a factor in how likely it is to get raised off of your call. This is something to remember when you consider your total equity.