Thanks for that excellent and detailed explanation. Just to clarify, given my situation, as long as I have a mortgage on my IP, it makes more sense to hold my bonds/fixed interest allocation in my offset account to avoid me paying more tax and because of the higher interest 'saved' for my money?
Yes. At the end of the day everything is just a tool used to build wealth. Fixed Interest/bonds is not the most effective use of your 'defensive' asset allocation from a total return perspective. You are going to get a greater return by keeping cash in the bank than by putting money in the bond market with the potential for capital losses in a rising interest rate market.
When the key elements are risk and return if you can get a better return with lower risk, that's a win. No point using a riskier asset for a lower return.