Deja vu.
Seriously, I think the Toyota sensor in AEM's wizard has absolutely no relationship with the GenIII MAP sensor (as, I guess, you're proving).
Ignore the equation, look at the graph - that should be everything you need. While AEM seems to publish nothing useful about what their offset & scale parameters really mean, there are some hidden ckues:
1) MAP sensors normally have a linear response, from (min volts) at <= min pressure to (max volts) at >= max pressure. If it's linear, all you (should) need are those two end points, and you have described the entire curve.
2) The other clue - take a look at how AEM models some 'known' MAP sensors (specifically, the AEM and GM sensors) in the wizard. "Load Scalar" seems to be the actual bandwidth of the sensor (nominally 3 for a 3 Bar sensor), Load Offset is normally zero. I can only guesstimate that the load offset is the difference (in some unknown units) from -1 Bar at (min_volts). in other words, if the sensor reads -1 bar at it's lowest setting (most do), the offset should be zero.
3) So... go back to the graph (not the equation), you can pretty much read off the end points... I'd go with an offset of zero to start.