How to add a fixed transaction fee to each transaction? Each time I send some bitcoins from Blockchain.info, it allows me to set a specific fee. I've installed bitcoind and I can't figure out how to add a 0.00013674 fee for each fee. 

I have read a few articles and I see the set fees is always relative to transaction size. So, I'm using paytxfee=0.00027348 in my config file.

Issue is this setting is producing:

sent amount=0.00106326 fes=0.0000618 
sent amount=0.00086326 fes=0.00006153 
sent amount=0.00106326 fes=0.00014166

I'm willing to have my transactions included in the blockchain faster. Any idea to tweak my settings to have this improved ?
If you want total control over the fee then you will need to build the transaction yourself using createrawtransaction - more info here: https://en.bitcoin.it/wiki/Raw_Transactions

However, it's important to note there was a relatively unnoticed change in the way paytxfee handles the fee calculation earlier in 2016 - see here: https://github.com/bitcoin/bitcoin/issues/7633