I recorded every team's PP% and PK% for the past 16 seasons and found the median for each season.
It seems like the medians are coded to oscillate between the lowest I've seen at 19.5% PP versus the highest at 21.5% PP, and 78% and 81.5% PK. Haven't seen any special teams median outside of those boundaries, but I'll keep recording.
The absolute highest full season PP% I've seen a team record is 30.9%, the lowest being 12.3% (midpoint of those is 21.6%). For PK% (excluding my team): highest is 88%, lowest is 68.5% (midpoint is 78.3%). Im sure people who've played more than I have will have seen percentages outside those numbers.
So, it feels like either special teams percentages are pre-determined to some extent, or are soft-capped and have an opposite reaction to ensure a steady median (meaning a 30.9% PP would result in at least one team being that much under-median, or several teams bearing that brunt collectively).
Off-topic, I've done the same thing with GF/game and GA/game but those numbers have noise because I've been the best at each for like 10 years straight
What Im also curious about, but haven't been recording, is what effect the Barrage tactic has and if the game will take a Adam Oates on your shooting% to keep your team from scoring 10 goals a game.