Do you have a link to the post where someone measured a brand new PIU with no accessories installed versus a ST?
I'm not convinced it's weight related.
But before we start, let's agree on some assumptions. Because the PIU shocks are more dampened, we can assume that the PIU springs have either the same or higher spring rate compared to the ST springs. If the spring rate is higher, than the ride height should be less affected by weight than the ST.
Now that we have that out of the way, let's take a look at some factory specs:
https://www.ford.com/suvs/explorer/models/explorer-st/
Ford specifies the "minimum" ground clearance of the ST model to be 8.3".
They don't provide any other curb weight other than 4,345lbs for a 2.3L (2WD) model. Obviously a 3.0L (4WD) model will weigh more.
Now let's take a look at the specs for a PIU:
https://www.ford.com/police-vehicles/hybrid-utility/
Ford specifies the ground clearance of the 3.0L EB model to be 7.2" which is almost 1.1" lower than the 2024 ST.
I will say that 0.5" of that is probably due to the tires because the stock sizing on a 2024 ST has a 30.7" to 31" diameter. The stock size on a PIU results in a 30" tire so the ST will sit anywhere from 0.3" to 0.5" higher due to a larger tire. It still doesn't account for the PIU being a full 1.1" lower.
https://www.autoblog.com/buy/2024-Ford-Explorer-ST__4dr_4x4/specs/
I wasn't able to quickly find the curb weight for the 2024 ST on the Ford site so I'm using numbers here.
Curb weight: 4,701lbs
GVWR: 6,160lbs
https://www.ford.com/police-vehicles/hybrid-utility/
PIU 3.0 EB GVWR: 6,500lbs. *This is significant because it indicates a higher spring rate than the ST models. This reinforces the assumption that the PIUs feature a higher spring rate than the ST models.
PIU 3.0L EB curb weight estimate = GVWR - payload capacity = 6,500lbs - 1,670 = ~4,830lbs *This number can be a bit fuzzy because it's not clear whether the payload capacity accounts for the constants such as the weight of a driver + fuel. Either way, 4,830lbs is not all that different from 4,701.
We have received a few brand new 2024 3.0L EB PIUs with no accessories installed so it's basically a bare bones interior. They still appear to sit distinctly lower than an ST with all its creature comforts, etc.
I think there's convincing evidence that the ground clearance of the PIU is not due to weight, but rather due to different (shorter but higher spring rate) coils.