The regulations for stopping the timer are much less specific than the ones for starting the timer.
Article A6 is about "stopping the solve" and this is the only part that says anything about hand position when stopping.
A6d) The competitor must stop the timer using both hands, placed flat on the sensors with palms down. Penalty: time penalty (+2 seconds).
There is nothing wrong with those timer stops, and no need to change anything in the regs on this topic. Unless you're saying that these should be +2, in which case I see no point in searching for additional ways to penalize people.
People don't understand the difference between A4 and A6. Acorrding to the regulations you have to start the timer with your palms facing down and your fingers on the timer. According to A4b STARTING the solve with your palms is a +2. In A6d it's described that you must stop the solve with your palms facing down, what part of the hand you use doesn't matter.