Flaw in Rental Property calculator?

[Michael Craig Anthony]

My client wants to buy a new home and rent out his current home. Current home value is roughly $258k - he refinanced last month at 2.75% / 30 year and owes $150k. 

The rental calculator uses the purchase price to determine property value (which is used to show valuation over time). If I use $258k for the purchase price, the calculator assumes a large down payment to arrive at $150k. If I use $150k for the purchase price, the analysis assumes the current value is $150k - so I essentially lose $108 in equity when showing valuation over time.

It would be nice to have the option to set the property value without assuming a purchase.

Am I missing something here? Thanks!