I took some measurements today to compare my ATEI-milled Glock 19 Gen 5 to my newly-purchased Glock 17 Gen 5 MOS using the stock MOS RMR plate and the CHPWS RMR plate. I measured from the bottom of the slide to top of the mounting surface:
ATEI w/ Trijicon sealing plate: 0.720"
MOS w/ CHPWS (no Trijicon sealing plate): 0.745"
MOS w/ CHPWS and Trijicon sealing plate: 0.757"
MOS w/ MOS and Trijicon sealing plate: 0.760"
The CHPWS flares out to cover the entire bottom of the RMR, so I don't think it needs the Trijicon sealing plate.
I really like my sight setup on the ATEI Glock 19 and wanted to see if it would work on the MOS before I ordered any sights. I use the Ameriglo GL-404 rear sight (0.304") and Heinie 3186F front sight (0.310"). Here is the co-witness sight picture on the ATEI Glock 19:
And here's the co-witness sight picture on the 17 MOS with CHPWS plate (no Trijicon sealing plate):
I should point out that I don't have the Trijicon MOS kit with the screws needed to secure the RMR to the MOS, so I left the RMR unsecured in both pictures to try to get a fair comparison. They both probably sit a little lower once properly secured.
As far as fit goes, I'm sure it's no surprise to most everyone that the ATEI cut is the hands-down winner between these three. Without any screws, the RMR doesn't budge. The CHPWS plate was an improvement over the stock MOS plate but still had some wiggle without any screws.