Update:
I also found out the rim holes on the the 1-piece 2403 AS toilet were not 100% opened completely. When I looked carefully, I noticed opening @ the far end was smaller causing even weaker water flow down to the bowl.
That's an obvious defect on the bowl.
I ordered another 2403 unit, and it arrived today. The rim holes on this unit were uniform and the holes went all the way thru'. However I still did not see the larger rim hole like the 2-piece AS Cadet 3 1.6gpf toilet I have in the other bathroom under the far tip of the bowl.
Using my wife's mirror, I took two pics.
This is the large rim hole on the 2-piece AS Cadet 3 1.6gpf toilet I'm talking about that's under the far edge of the rim.
The 1.6gpf AS Cadet 3 2-piece toilet flushed toilet papers along the far edge swiftly (w/ or w/o the automatic bowl cleaner installed inline).
This is the same rim area on the 1-piece AS 1.28gpf 2403 Compact Elongated toilet (small rim holes):
This new 2403 unit filled the toilet bowl more compared to the defective unit I had, but it only succeeded 50% of the times in flushing toilet papers around the far edge. Comparatively, it did do a better job than the other unit which I think was definitely defective (rim holes not open completely).
(BTW I no longer connected to the automatic bowl cleaner in the tests on the new 2403 unit.)
I think the 1-piece is an elongated bowl and it makes the flushing problem worse w/o that larger rim hole to supply more water to flush down toilet paper(s) around that far edge.
Anyone can shed some light if a 1-piece compact elongated 2403 unit does have a large rim hole around the far edge.
Otherwise, at this point I think I'm hitting a design defect of this toilet.