Estimating Assembly costs II
It's not easy to have one answer.

There are several factors to take into account.

Imagine you have 4 A components in your BOM and one B component. If you replace B by A then you'll end up with 5 A and 0 B. The less component you have the higher unit price, so you optimized the unit price by removing B and adding 1 unit to A so A unit price should decrease.

But it's difficult to estimate the optimized quantity. Component price will follow kind of log curve. So if you have already 100 A units and add one instead of B, you'll only save on B price. A price won't decrease much.

Also if you can remove a significant number of reference, assembly house will need less round to place components as placing machine have limited slots for component reels.
So you need to discuss with the assembly house how many reels and tray they can have in placing machine.

Price optimization is also dependent of overall quantity: if you're doing a 500 board production with around 200 components/board then overall quantity is not that much and it will be difficult to negociate prices.
But if you're making consumer electronics, then BOM optimization is dependent of purchasing department, as they will put coefficient on components regarding their price.