The target should be blury. The front sight in focus.
While I just starting shooting anything this past week I have been wearing bifocals for the last 2 or 3 years. Prior to that for 4 years or more I wore one prescription at work most of the time that was for reading and computer screen reading and another prescription for anything else when not working in the office at work or when not on a computer at home. I learned after I got bifocals that some lens shapes and sizes are better for bifocals than others. I also learned that while some may say it will only take a little time to adjust to bifocals it may have taken me 6 months or more to be comfortable most of the time wearing bifocals. I now only use the computer glasses when working on my car or other activities where it is difficult to view through just the lower portion of bifocals when working up close to something. So I think some people may need to give bifocals or trifocals more time. It takes time for the eyes and brain to adjust to the lenses.
If you use reading glasses, I got some full lens safety readers that work well.