I got 777800 on Syncopia with clearing 70.8% of the mines, so yes I would say it is possible to get 1 million points, but your clearance score will have to be close to 100%, or you just keep getting high chain bonuses.
I personally think that for now the clearance will stay around that, 60%, but you must work on your accuracy. I get a lot of 5-Chains myself, but 10-Chains are rare and 15-Chains even more. I suspect that if I could get more 10s or 15s, with the current clearance score I would've done a higher score.

Also, have to figure out whether clearance score talks only about fresh mines, or old mines count too. 30% missing seems a lot for what I essentially missed on stage 14, so I think this "Mines Cleared" column refers only to fresh mines. Since you have to target those in priority, it would make sense.