I use the AP/Arista/Samigon reels that have the wider flanges, but work with the Paterson tanks.
I load the first roll of 120 into the reel. Once the full roll is loaded, I continue to push it further until the leading edge reaches the core - it stops there.
I then load the second roll untill it is fully on to the reel.
The rolls don't overlap - they both develop fine.
This does not work with either rotary agitation or agitation using the turning stick - that will cause the film to move in the channels of the reels, and may cause the rolls to overlap.
It does work with inversion agitation.