It is highly likely that at least one of the opertor is bidding for 15Mhz, i.e. 10Mhz plus 5Mhz, that's probably why bids are going high.
Since there's no increment in 5Mhz block lot so far, this even looks more likely.
Again, this is just speculation. Nothing can be said for sure before the final results.
Total increase in bids in value from base price is currently standing at US 17.82 million dollars.
Just to mention again, the base price for four lots for 2100Mhz was 885 million dollars.