I got it - Samsung Flash Imager (attached) is the tool for finding the offset. Unlucky the program is not in English
1. Click on the first menu item and select the first option (ends with the word "flash").
2. Select to view "All files" and find your CG1.smg
3. After that back on the main program screen in the down-middle select 16bpp from the drop down menu (default is 1bpp black and white icon).
4. Under it there are two text fields with signs (0...128 and 0...185) - type 176 and 220 there (I think these are your screen dimentions)
5. Click on the first button under (in the left of the ^ button). A scrambled colored image will display on your screen
6. Now start clicking on the + buttons up... Try them one by one and you will see what they will do - they will move the image up. Some of them will move fast (frame), some of them slow. Go for it until you see the "Hello Moto" bootscreen picture.
7. When you find the bootscreen picture it is now extremely important to position top left corner of the image in the exact top left corner of the preview. No even single pixel up or down!
8. You will see the offset under the 8 buttons. It's 6 digits with A-F letters combination.
9. Open the offset.ini of bootscreen replacer and create what profile for your phone (self explanatory).
10. Replace your image and enjoy
Oh and don't forget that the image must be in the same format - same dimensions and same color 16bpp...!!!
P.S. That's the MOST WEIRD tutorial I've ever wrote!