2021 IPC Table 1106.2 increases allowable flow from 2012 IPC Table 1106.3

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Sorry for the duplicate, first posting and didn't realize that it might take a day for moderator review if you add attachments.

2021 IPC changed Table 1106.2 Storm Drain Pipe Sizing from roof square footages to gpm. The new chart allows significantly greater flows, yet I haven't seen this mentioned anywhere.

e.g.
The 2012 IPC (what we use for Indiana) has a 4" horizontal pipe at 1/8" slope capable of serving 2,506 sf with a 3" rainfall rate/hr. That code also includes the equation gpm = 0.0104 x R x A, where R = rainfall rate and A = roof area. Doing the algebra, that has a 4" pipe capable of flowing 78.2 gpm.
The 2021 IPC table has the same pipe size and slope capable of 115 gpm. 2021 IPC 1106.2.1 has the same equation GPM = R x A x 0.014. Doing the algebra there and it's saying that pipe could serve 3,684 sf with a 3" rainfall.

I realize that roof drain manufacturers changed their engineering info to gpm's, and that's perhaps the reason for the code change to gpm's, but I haven't seen anything to explain why they changed the allowable flows for the pipes.

thanks
Ed