The headline payout is one of five numbers and it's the least interesting one. What you want is effective revenue per hundred clicks, and you cannot get that from a dashboard, you have to run it.
What differs between two networks carrying the same advertiser:
| Variable |
Effect |
| Payout |
the number you're looking at |
| Approval or scrub rate |
can move effective by 30% on its own |
| Cap and pacing |
a high payout you can only run to 40 a day is not a high payout |
| Hold and clawback window |
changes when it's yours, not whether |
| Geo or source restrictions |
B may pay 37 on tier 1 only |
My honest guess on your specific case, and it is a guess: B is a smaller network buying volume to hit a tier with the advertiser, and the 37 will be 31 in six weeks. That's the most common shape of a 30% gap.
Don't move everything. Send B 25% for two weeks, hold the rest on A, and compare net paid per hundred clicks after the first payment clears. That's a fortnight and it costs you almost nothing.