The power on delay means that after it sends the TV on command, it will wait 2.1 seconds before sending other commands to the TV (such as input select). The inter-device delay is used when sending multiple commands to the same device (after power on).

Since your Sony seems to work very quickly try changing the power on delay to 300 ms, then increase it as necessary until the TV always works (powers on and selects the right input). You can also decrease the inter-device and inter-key delays as well.

The harmony will try to reduce the overall time required by ordering the commands for devices with the longest delays first.