Please note, this is something of a duplicate of https://bugs.mojang.com/browse/MCPE-60245, but the response there is incomplete, and not applicable.

As described in the linked ticket, a minecart with hopper will pull from another minecart with hopper if it is one level up and to one side, but only in the Bedrock versions of Minecraft. The Java edition of Minecraft does not exhibit this behavior. There is no expectation for this behavior to be the standard; it is illogical, and does NOT match the existing behavior in the rest of the Minecraft codebase. If this were truly "working as intended", it would be this way in both places.

The statement of the minecart with hopper pulling in items from a slightly wider range than the cart itself does NOT explain this behavior for two reasons:

1. It is not collecting loose items; it is pulling from another container at a MUCH farther range than it should.
2. The size of the minecart is smaller than a block, so your calculations appear to be starting at the wrong place, and are basing it from the outside of the block the minecart is sitting in, and NOT from the width of the minecart itself.

This is not a matter of a feature request; this is getting the behavior corrected to do both what is described in the Wiki (which it does not right now), as well as match the other half of the Minecraft codebase.