How to check if one particular part is in region3 trying not to use FindPartsinRegion3?D

The reason I dont want to use FindPartsInRegion3 is because you need to loop every single part and check if part is in it

Here's what im trying to do.

I have a placement system and If the part will be in Region3 I want to place it. If the part is outside the region I dont want to place it.

If I used FindPartsInRegion3 i'd have to make a block and precheck if it is in the region before I place it for the player.