Why East India Company convoys were difficult frigate targets

Wouldn't East India Company trade still be vulnerable within American frigates' reach?

The ships were large and heavily armed, and they usually travelled in sizeable convoys with warship protection.

Reaching an East India Company ship did not make it an easy prize. A large armed Indiaman could itself demand a difficult action from a frigate, while several travelling together increased the danger. Company convoys could contain up to thirty heavily armed ships and an escort. Other merchants could pay to join, helping account for convoys that grew to around a hundred vessels. Merchants sailing independently to save time or avoid convoy costs accepted greater exposure to raiders.