EPCM Custom Calculation Rule - Mark up for multiple entities in a single rule

Summary:

Can we create single custom calculation rule for marking up cost by x% for multiple entities?

Content (required):

I have 50+ entities and cost of each entity needs to be marked up with 3% of respective entity cost. When I created a single custom calculation rule with parent entity, 3% of total is calculated and allocated to same entities instead of 3% of its respective cost. See below example for more clarity

So I had to create 50+ separate rules for marking up. Is this the only way? Even though execution time is much less, I wanted to check if I can reduce the number of rules which will reduce future maintenance process.