I'm mining on the testnet and I noticed that the reward is more than 5 (near to 5.2) Ethers for some empty blocks I mined. I thought the reward was 5 + tx. fees. How can an empty block have a reward more than 5 Ether?
There were uncles in the block.
Without links to the specific blocks are talking about it is difficult to know for certain.
However, there is the potential that the block you are looking at may have also included some uncles.
The miner will also receive an award of 1/32 per Uncle block included. Uncles are stale blocks with parents that are a maximum of six blocks back from the present block. Valid Uncle blocks are rewarded to halt network lag (time to propagate a valid block to the whole network). Uncles included in a block receive 7/8 of the static block reward – or 4.375 Ether- with a maximum of 2 Uncles allowed per block.