Ideal Margin Usage?

 

What do you traders feel about trade size?

For me, on a 50:1 leveraged account the perfect size seems to be 40% of free margin used in total and starting out with 20% on initial position.

That seems to give me enough room to scale a trade up to 40% usage if needed, but enough risk so that I don't need an insane winner to get a good % gain on balance. 

The only challenge is figuring out how many lots will equal that type of risk and sometimes it has to be estimated based on the currency pair. Different pairs take up different margin per lots.