Why are all values ​​overwritten when overwriting the list property values ​​in the Bitrix infoblock element?

Question

1C-Bitrix

Good evening. There was a small problem with changing the values ​​of the infoblock element properties using the API.
I have the following code:

$property[1] = Array( 
'HIT' => array($bNewS, $bHitS), 
); 
CIBlockElement::SetPropertyValuesEx($el["ID"], false, $property[1]); // обновляем дополнительные свойства

The essence of the code is as follows: we take properties from the array and overwrite them in the infoblock element.
The point is that the HIT property is of type List.
And inside this list there are the following parameters.

$bNewS, $bHitS are the IDs of the values ​​of the list, respectively 81, 79
Well, when I execute the SetPropertyValuesEx query for the values ​​of the list, then all the values ​​that are in this list are overwritten, but the values ​​I set are replaced as needed.
How can I make sure that these values ​​that I did not set in the array are not overwritten?