There are photos here on this board comparing pre and post advisory Regents, and they are the same. The general consensus is that the requirement of the recline bar makes kids fit with less growing room than a pre-advisory seat installed without the recline bar.
I own a post-advisory Regent, and I measure right around 20 inches for the top slots. H has a 19 inch torso measured against the wall as of two weeks ago, and has an inch before getting too tall for our Regent, installed in my Focus. She is an inch over the Frontier and Nautilus top slots, which measure 18-18.25, depending on who measures. (See
this thread for comparison pics of her in all three seats)
This is how much growing room H had in the Safeguard a full year, 3.5 inches of total height and a little over an inch of torso height ago. I wish I'd tried her in the Safeguard again on the day I took the Nautilus and Frontier and Regent comparison photos, but I didn't. Knowing how she grew, though, My guess is she is exactly even with the Safeguard's top slots, while being an inch over the Nauti and Frontier's, and having an inch to go in the Regent. :shrug-shoulders:
There is such a varying degree to the recline of the Regent, depending on how the recline bar fits in the vehicle, so I can see a child having less than 20 inches of torso grow room in certain situations. In ours, though, the 20 inch measurement holds true, compared to my daughter's seated torso height against the wall, and compared to how she fits other 18-inch top slot seats.
Britax's top slot height measurements and their seated shoulder height allowances have had discrepancies for awhile now, and not just for the Regent.
They say 19.1 for the tallest harness height, yet they say 20 inches for the maximum seated shoulder height allowance, yet they don't allow shoulders over top slots.
Something is obviously wrong there. All I know is, I measure 20 inches, give or take half an inch due to the massive huge harness slot holes on that seat, and my daughter's torso height is 19 inches, and she has an inch to go in the Regent, and she's an inch over seats that measure 18 inches.