Amazon Affiliate API / PHP : how to get products with savings?

Question

I would like to fetch all products with a price reduction from the Amazon Affiliate API in PHP.

I have been regularly using this API for some time but it looks like some of my parameters in the payload are ignored.

With the following payload:

{
 "SearchIndex": "Computers",
 "MinSavingPercent": 10,
 "ItemCount": 20,
"PartnerTag": "****",
"PartnerType": "Associates",
"Marketplace": "www.amazon.fr",
"Operation": "SearchItems"

}

I get 10 results (while I wanted 20), most of them have a price reduction.

If I change the category like this:

{
 "SearchIndex": "Books",
 "MinSavingPercent": 10,
 "ItemCount": 20,
 "PartnerTag": "****",
"PartnerType": "Associates",
"Marketplace": "www.amazon.fr",
"Operation": "SearchItems"

}

I get again only 10 results and none of them has a price reduction.

Am I missing a parameter somewhere to make sure I only get products with a rebate? For those products without rebates, I see that the node for price savings is not even there.

Or is there another way to achieve the same goal?

Thanks