Ok, thanks for clarifying. What frame size are you interested in? You said 52, but they make 51 and 53. I assume you want a number better than a guestimate? For the 53 at least the effective TT is 535. The seat tube angle is 74 degrees. The setback at the seat tube top is then

SB=530*cos(74) = 146 mm.

The distance from the BB to the front of the effective top tube is

ETT-SB = 535-146 = 389 mm.

If the bearing stack refers ti the distance along the top tube from the center of the TT intersection to the upper end of the headtube, you need to subtract 30*cos (head angle) to compensate. The head angle is 71.5 degrees, so the compensation is about 9.5 mm, for a reach of 379 mm. So about 9 mm longer than your calculation. I don't know exactly what we did differently, but I didn't see a column for a 520 mm frame.