Hi, had the same problem for a while when I switched to thumb shooting. I solved it by aiming 'inside the bow' .
I just gap shoot by aiming with my arrow point. I'll try to find a pic online that describes it better. It is properly explained in 'Saracen archery' if I remember correctly. I thnk 'Nu Sensei' has a video about the three aiming metods (outside the bow, through the bow, inside the bow).