How to change "Emitter type" for water content estimation?

https://communities.bentley.com/products/building/performance/w/building_performance__wiki/31381/pipe-sizing---water-content-for-heating-and-cooling-emitters

On the page above it implies you can change emitter type for your water content calculation. I know the water content calc is just  an estimation but how do you change your "radiator" to "other emitter" on Netsys? (This is for a heating system).

Also, what are these formula based on? Is there a standard that is used such as a British Standard?

Lastly, what type of emitters are comparable to "other emitter type"? I.e, is it suitable to estimate the water content of fan convectors or radiant panels, for example? 

Currently I don't understand how a single formula can represent multiple emitter types in terms of water  content.

Kind regards and thank you