I can say there are some things to keep in mind about AP rounds. I usually mention the 2 most important things, but I'm going to start reminding people of three things: the 2 biggest trump cards are range and angle of impact. Also, sometimes armor works.
Trust me when say I know it is frustrating. The best thing I can suggest to to know the AP capability of the round you're firing, an approximate angle in which your rounds are impacting (that can be very difficult due to terrain variation, the small window of time a person has to observe an impact, the angle of the armor of the target vehicle, and the directional facing of the target in question). In a perfect world, your AP round would impact perfectly at °90 ll the time and you'd get the absolute best AP performance available, but there are too many trump cards being played.
Also, I did some digging in to the effectiveness of AP rounds (this does not pertain to lyric's issue though), and though I could not find exactly what I was looking for I did find some information laterally concerning the AP ability of certain projectiles over various ranges. For instance, some of the most common rifle calibers in the world such as the 5.56 NATO (both variations), 7.62 NATO, 7.62x39 Soviet, and 7.62x54R Russian, have all been tested for best penetration capabilities over multiple range against multiple kinds of mediums. I do not have the data in front of me and I will have to dig it up again, but from memory I remember that on average but the best range for the 5.56 NATO for penetration was 200 yards, anything closer and the bullet shredded and broke apart and anything further away the kinetic energy started to decline. The 7.62x39 Soviet performed best in the low 200's yards. The 7.62 NATO did its best penetration in the upper 200's as did the 7.62x54R Russian. The point of all this is simple: I believe that when fired "close", there is a chance that the AP ability of a projectile can be reduced thanks to the mass times weight vs object integrity thingy equation.
I try my best to know the abilities of every tank out there. If I'm in a Panther, I'm not too worried about anything outside of 1600 yards to my front except a King Tiger, Firefly, Tiger, or another Panther (and in that order). Not that it can't be done, but the odds of everything being perfect enough for a Panzer IV H and lower (yes, the Panther IV H has better AP than all other tanks in AH except the 4 mentioned above), defeating the Panther from the front beyond the 1600-1800 yard mark is slight. Take it with a grain of salt because there are always exceptions to the rule.