This dramatically increases the economic benefit for the investor. 

That's the SIMPLEST way to increase yield: Lower down payment.

Do they increase or decrease due to supply or what?

Hey Ron I'm an investor in Nashville, and with the market booming the way it is with the population increasing one thing a lot of investors say is the demand is high and the supply is low making this a sellers market.

I personally was targeted by a tenant group that spammed my google reviews trying to avoid a small rent increase....those reviews are not as telling, but management never returns calls, property owners complaining of similar things are very telling.

What other options do I have besides a HELOC (which I am also considering, but holding off on because my mortgage payment is so low and I know with a HELOC it will increase).

@Caleb Heimsoth Right when we bought the condo the HOAs increased by 15%.

I want my home value to continue to increase.

It's so very refreshing when I come across an agent who has information ready and available to me and subsequently my investor.

It is more difficult to find properties whose value you can increased significantly while keeping as a rental, especially in the NY area where properties hardly cashflow.