Perceived Lead will:
-vary as YOU gain experience.
-vary from shooter to shooter.
Applicable no matter if shooting Pass/ Swing thru, or Sustained lead.
I understand this does seem to help you much, I do apologize. My best advice is to :
1)Proper Gun fit
2)Qualified Instructor /Competent shooter that can instruct.
3)Observe/ be observed.
I and other shooters/ instructors will advise "you just smoked that target, stop and ingrain everything you just pictured, everything you did".
Rules: One cannot hit what they cannot see. NEVER allow the bird to get under your muzzle, most misses by newer shooters are shooting over the bird. Second most missed is shooting behind because the bird "beat" you and you never caught it. Third ( believe it or not) is shooting in front of bird. They are improving and shooting too far ahead. Thinking they have to shoot that far ahead as they did before - not realizing they have improved and are aquiring bird quicker.
I can stand and watch a shooter and by watching determine why he missed, and read the 'breaks / chips'.
With persmission, just watch better shooters whom shoot your style ( pass. sustained) just stand back behind, don't crowd and get the rhythm and get a feel for "perceived lead". This is why if in a tourney,and someone is having a bad day - do not watch them shoot, it will mess YOUR game up.
As we know from pad to center stake is 21 yds. I shoot low gun btw, and when I started say from station 4, I didn't break the bird until about halfway past the center stake. I got to where I never missed 4. Then I did, I was gaining skill and was missing in front.
My perceived that used to work, now had to be changed, I was getting on the bird faster, and had to change my perceived lead.
Low gun, gun fits, smooth gun to face,and smooth became fast, I was seeing NO lead, and breaking it BEFORE it reached the center stake.
I was "on it" ,'passing thru it" and "slap!"
All I see is the very most leading sliver of target. I swing extremly fast. Folks able to "read me" says it appears I am only 2"-6" ahead of bird when I slapped trigger. Depends whom is "reading" me shoot...different folks percieve the same view different. This is station 4.
Low 7 there is nothing but dust because I hit about 1/4 the way out of the house.
Low 6, I break about the same way...on doubles I have time to smoke a cigarette waiting for H 6 to come on over. <taps foot, smokes, checks watch, 'any time now, I'm waiting">
I'll break the second bird on doubles at 6 between 1/4 to the low house to 1/8 in. Let the bird come to you, nail it.
Just like leading a spray from a garden hose - once you catch what ever it is you are trying to spray ( neighbors pet, kid running in the water, a ball being rolled) your human computer remembers the perceived lead and you "know".
I am dead serious about this gun fit to shooter, and doing 25 repetitions a day and dryfiring. Get slivers of orange tape to replicate the leading edge and practice smooth swing, pulling thru , slapping trigger and FOLLOW THRU.
Garage, spare room, warehouse...just practice 4 rules of Safety and Rules for Dryfire Practice. Actually having that sliver of orange to focus and train your mind and body - really really works.
Human Computer will remember - like Zen you will do this on the Skeet Field.
HTH
Steve