are you assuming I have the full sum at the start and am either lump sum or dca buying?

If so, depending on the time frame, you might need to factor inflation into the DCA time frame.

For example, say I had 100k cash in 2020 and assume a 5 year time frame for the dca model. There was around 20-30% inflation. That's a significant cost for holding the lump sum that probably should be factored into the dca model.