Expectation bias? You're preaching to the converted there. I had a number of T50rp headphones I was modding and thought I was making huge improvements on one particular set. After about a week, I decided to work on a neglected set of modded T50RP. I compared my new favourite mods against the neglected mods and I could not tell the difference. it was very deflating.
In this case, I have both the Project Polaris and the RJM Sapphire on my desk and I switch between them regularly. Last night I did a bit of A/B testing (granted, the testing was not blind and I was spending about 10 seconds switching cables) before I decided I should make my update this morning. Either the Sapphire is drifting in a negative direction or the Polaris is now sounding better.
I personally wouldn't think that the actual performance of the amplifiers is changing, but rather your brain is getting better at picking apart the subtle differences. just imo! :)
glad to hear that you are liking the product regardless haahh