@Outlander  mentioned the possibility that umps are calling higher strikes than normal against Sal Frelick as a reaction to a particularly impactful missed call against him in Wednesday's game against the Angels. The Ump Scorecard:

I couldn't find a quick way to visualize strike calls against Frelick that were mapped to his personal strikezone, so I decided to make one. Using Baseball Savant's search, we can pull the data from strikes called against him this year.

The x-axis should be ideally be consistent for all players, though with Frelick being a left-handed hitter, he might be more likely to get the outside strike called against him. Then I looked through the video and found the Z values of the pitches that were right at the top and bottom of the strike zone on screen. They do seem to match up with the rule book definition:

Quote

The Strike Zone is that area over home plate the upper limit of which is a horizontal line at the midpoint between the top of the shoulders and the top of the uniform pants, and the lower level is a line at the bottom of the knees. The Strike Zone shall be determined from the batter's stance as the batter is prepared to swing at a pitched ball.

Here are the most borderline top and bottom pitches:

Top at plate_z = 3

Bottom at plate_z = 1.31

And here are all the called strikes against him this year, viewing the pitches from the batter's perspective, so Frelick would be standing on the right side of this plot.

There are quite a few high strikes getting called, but is that abnormal? If we set the zone of interest between +- 1.04 in the x-direction and 3-3.37 in the z-direction, Frelick has taken 23 pitches, with 14 called strikes and 9 called balls. All of the pitches called balls are either inside or outside. None of the balls over the heart of the plate are called.

According to Baseball Savant's Delta Run Expectancy, those high strikes are responsible for -0.856 runs. The most impactful was in the Tigers game against Beau Brieske, when Frelick had two runners on an dropped from 2-1 to 2-2. I couldn't find win expectancy values, as the impact to the game on this one was minimal with a 10-0 score at the time.

In this particular area of the zone, the MLB average is 28% ball and 72% strike. Frelick is 39% ball and 60% strike.  But that doesn't account for the height of the player. Frelick's average strike zone top is around 3 feet, but Aaron Judge's is north of 4, so we would expect him to get more called strikes in that area. If we filter down to players that have an average strike zone height below 3, we come up with six players: Garrett Stubbs, Jose Altuve, Frelick, Nicky Lopez, Nick Madrigal, and Miles Mastrobuoni.

Their collective percentage of balls to strikes in this zone is 48% ball and 52% strike. Of the six players, only Jose Altuve gets the ball called more often than the strike (67% balls on 27 pitches).

It's hard to say with this information how much it is affecting Frelick, but it does nevertheless show that shorter players are forced to expand the upper part of the zone, unless you're a former MVP, 8-time all-star, 2-time World Series champion, and 6-time silver slugger.