The BOV doesn't really work the same way. The wastegate works off of the pressure difference between the atmosphere and the intake piping, so it regulates boost (which is just pressure above atmosphere). The BOV works off of the pressure difference between the intake piping and the intake manifold, so it opens when throttle plate closes (manifold vacuum). That being said, there are a few things that can affect whether the BOV works properly or not.

First, there is often a preload adjustment that changes how much pressure difference there needs to be on either side of the BOV actuator/diaphragm before it opens (one side is the intake piping, the other side is the vac line port). So that preload adjustment could be set really high, and in that case you wouldn't have enough boost and enough vacuum (at the same time) to get the BOV actuator/diaphragm to open. Go to the website of whatever brand you bought and look up the procedure for setting that. Some vendor websites have that info too, so see what Google comes up with.

Oh, try to stay away from Tees and things like that on the BOV vac line. Tees are often pretty small inside, and don't do great things for pressure drop. The boost gauge doesn't need any flow to make it work properly, but the BOV does. It's kind of like electricity. Something that draws current will make a voltage drop across a wire that is too small, but it doesn't matter with a voltage gauge or multimeter because it takes a really tiny amount of current to make them work. No current draw, no voltage drop. With the vacuum line, no flow means no pressure drop.

Second, make sure the vacuum line going to the BOV is not too small and not too long, because that can make a lot of pressure drop and can affect how well the BOV works. That's not generally an issue though, because any vac line that properly fits on the BOV nipple and isn't strung all over the engine bay is generally more than adequate. The preload adjustment is the likely cause of your problem.