I agree with you and Albert, but this doesn't solve the problem of the reservoir being lower than the callipers/wheel cylinders when fitted directly on the master-cylinder.
So, if the position of the reservoir is not a real problem, unlike Albert says, yes, one problem does exist: the height of the reservoir. That is the reason why I chose to remote it in front of the bulkhead panel. It is also much easier to check the level and refill.
After, it can be considered as being very picky to think about an eventual leak, but I thought it would be good to mention it.