Well, we're getting closer to solving this mystery!
Building height taken from the most recent drawings submitted to the City for approval, available on the City website. Here's a zoomed in image that shows the height at 425':
Now here's a zoomed in image of the lower part where they start the measurement from. The measurements begin 2 floors below ground level because the base is exposed on the bluff side of the building. So because the backside of the building is exposed on the bluff that is where they started the measurement. here's the image:
So, from all of this I take it that from ground level on the Prospect Ave. side of the building the height is going to be roughly 325' but on the bluff side of the building they are adding another 100' because the parking garage, pool, spa, and gym are goiing to be built into the bluff. It's either that or they are starting the measurment from the base of the bluff, either way, I would go for the 325' ground level before I would the 425'.
Just to illustrate better what this is all saying, here are 2 more renderings that shows the difference between the Prospect Ave. side and the bluff side of the building. No on=ther high rise in the near eastside skuline is built like this into the bluff.