Card-not-present is a different rate
A payment where the card is not physically present costs more to accept, because the fraud risk sits with you rather than with the terminal. If you are comparing an online rate against your in-store rate and wondering why it looks worse, that is why.
It also means a single blended rate covering both is almost never competitive on both. Worth seeing them quoted separately.
Gateway, acquirer, and who you are actually paying
Online acceptance usually involves at least two parties: the gateway that presents the checkout and passes the transaction on, and the acquirer that settles the money. They can be the same company or different ones, and they can each charge you.
Merchants are frequently paying a gateway fee they no longer need because the platform they moved to already includes one. It is a common and easily recovered cost.
What to check
Whether it works with the e-commerce and accounting software you already run, because that constrains the field more than price does.
What a chargeback costs you and who handles it. And whether a hosted checkout is enough, or whether you need the payment to happen without the customer leaving your site — that changes both the cost and your compliance obligations.