Packaging strategy "Calculate" always returns "There are no shipping rates available for this address."

This also affects 2.x but the REST API responds with a much more useful error message:
Total package count cannot exceed the limit of {PACKAGE_COUNT} packages.

Examining the request sent I see:
'groupPackageCount' => 98891

There is only one package. Examining $requested_package_line_item->sequenceNumber the value is 1

The group package count is set using $requested_package_line_item->setGroupPackageCount($count) and $count is calculated with static::calculatePackageCount($requested_package_line_item, $packages[$requested_package_line_item->sequenceNumber - 1]) which gives a result of 98891.

This is a result of the default 1x1x1mm package being selected.

If the configured box is smaller than the items going into it this math will work out a huge number of packages despite it being an impossible shipment.

If we don't want to introduce anymore complexity into the Calculate option then at least the description needs to be changed to something like:
"Calculate" will take the volume of the package type selected in this shipping method and divide it by the total product volume of the order. Fedex will return a single rate for the number of packages with the selected dimensions and weight evenly divided between them.