To be fair to BitPay, the fee might be higher when they need to spend the coin they receive in what could be weeks in the future.
They could be combining unspent outputs/spending when transaction fees are low, they're also probably big enough that they could get fiat first from someone else and then settle the bitcoins with them later.
That could wind up being a lot of fiat. As in 10s of millions of different countries money across the globe. It's easy to say they can combine when fees are low, but if
BTC has an up or down swing that causes fees to be high for a week or so it can start to become an issue. Most of their clients get fiat the next day. If fees are high and
BTC is down 5% they now either have to float it and hope it goes back up or eat it and take the loss.
A couple of weeks ago I got a new laptop from newegg
BTC at that point was $11825 give or take a buck. Within hours of my purchase
BTC was at $11,400 and fees were stupid high and would stay high for a few days after too. Guess what newegg got their money in their account and didn't give a shit.
So, their business model requires them to have to be able to move in the next block and you get to pay for that.
We, can argue if it's a good business model or not, we can argue if it's a sustainable business model or not. But it is the one they choose to have.
So their additional fee if you look at it, tends to be the
2x highest fee needed to be in the next block over the last few days. Note, not the average highest fee, the highest fee.
Around here, some gas stations charge more to take credit cards because they have to pay the 3%+ fee to take them, so they pass that to the consumer. You can accept it and pay with your card or pay a bit less with cash or drive to the next station. Same with merchants using BitPay.
-Dave
Edit added
2x above about 15 minutes after initial post. Brain freeze on my part as they tend to move your
BTC after 1 or 2 confirms and then move it again later. Not sure why.