And by the way, I wouldn't use CDM to solo mine. When you solo mine, you don't want 36 or 72 seconds per hour not mining for yourself because in this time it can be when you're gonna hit a block. If you are pool mining then it is ok because shares you will be hitting a lot anyway. I'll give you an example: a few months ago when I was still solo mining, I was gonna stop one of my rigs and in the time between hitting CTRL and C this rig found one block.
Your logic is incorrect. Miner will send 1% or 2% of mining time anyway - pool or solo modes. Probability to find the block in solo mining when miner is busy in devfee mining is the same 1% or 2%.
So check your math again.