[Needs Help]

Do you know your old center of bottom bracket to seat top measurement? If you do, you can calculate how much further behind the bottom bracket the new seat tube angle puts you.

As far as I can discern, what happens forward of the bottom bracket has no effect on your setback. For instance, you could take your old bike and weld on 5 cm more of top tube length, change the stem length to 150mm, and change the stem angle to -17 degrees, and your setback would remain unchanged: your seat tube length would be unaffected and your seat tube angle would be the same, so you would be sitting in the same spot relative to the bottom bracket. All that would have changed would be the front of the bike got longer, and the handlebars were in a different position. That wouldn't affect where your butt and knee cap were positioned unless you scooted foward on the saddle to enable you to reach the bars.