Question about Upgrading Cloak of Resistance

One of my players has a Cloak of Resistance +1 and wishes to upgrade that to a Cloak of Resistance +2.

The crafting cost of +1 is 500gp and of +2 is 2000gp. The difference is 1500gp.

But the item is slotted (shoulders) which, as far as I can tell incurs an additional 50% cost, making the upgrade cost now 2250gp, more than the cost of just crafting a +2 outright.

Is this correct? I'm looking at the section of the rules in CRB, page 553, 'Adding New Abilities' that reads:

If the item is one that occupies a specific place on a character’s body, the cost of adding any additional ability to that item increases by 50%. For example, if a character adds the power to confer invisibility to her ring of protection +2, the cost of adding this ability is the same as for creating a ring of invisibility multiplied by 1.5.

I believe the 50% increase is only for additional abilities and not increasing the bonus of an existing ability. That's how I've always done it anyway.

Well, certainly in light of the cost discrepancy it is how I am planning to do it, but I was trying to see what if anything I overlooked. :)

Yup. That +50% is for adding additional benefits.
For an example an item that adds +4 to two stats. The first +4 would be priced normally, but the second +4 would incur the +50%.

the crafter has to pay only the difference between the cloak +1 and the cloak +2, that beig 1500 gp, it matters not that it´s slotted, he is upgrading an existing item, not adding another power/boost/bonus, same with weapons, armor, ring of protection, amulet of nat. armor atc

Yup. That +50% is for adding additional benefits.

For an example an item that adds +4 to two stats. The first +4 would be priced normally, but the second +4 would incur the +50%.

Like upgrade "Belt of giant strength +2"(2000gp) to

Thanks for the feedback everyone. I appreciate the clarification. :)