Trying to forecast the trajectory of rising mortgage rates is complex due to market variables like inventory levels and potential interest rate shifts.

A lot of variables to consider.

Let's compare the difference between down payments only, of course there’s more to the money involved and variables on interest rates and type of loans you are using.Let’s just stick to down payment as a passive investor.

Of course there are many different variables and personal preferences definitely play a major part. 

Some variables conspire to trip you up Even if you know what you're doing.  

His variable expenses (taxes, insurance, repairs, etc) are only going to go up!  

HELOCs have a variable interest rate, allowing you to take advantage of declining rates without refinancing. - Perhaps you want to use it multiple times over a long period of time.

To me, reducing risk is about eliminating variables -- and IMO you have too many.

I think your trying to figure out your real after tax income on w2 earnings vs rental income earnings, but for that you need to consider all benefits of real estate and benefits of w2 which has much more variables then just this 

Lots of variables.