Stacking works. 2x MFGC 2.1L.
Reader is under the table facing down. 1 MFGC, unable to read thru my hand to the Apex Flex. One on table, and one on Apex, able to read with my hand about 1/2" off table. Flipped over, can read about 3-4" above table.
Edit: But note, repeaters are spaced out a bit. With them “stacked” stacked, it doesn’t really help much. If I had more, I’d try making an “NFC Repeater Cannon”.