The current plan is to place most of the weight eg battery, mobile phone, into the head and have a mostly empty middle section to get the height up to 1m. Why weight at the top - isn't that top-heavy? Why give it extra height - wouldn't it be better to make it shorter to save weight?
In this video, John compares this with balancing a 1m rod on his finger. Adding the weight of a mobile phone at the top gives more stability because of inertia and leverage effects.
Note that The Mocket will not have tail fins because (1) it will not move fast enough on the way up to be able to use air pressure as a stabilising force, (2) it has fold-out "head fins" which act as air brakes on the way down and tail fins would work against these.
One of the many experiments for The Mocket is to try to keep it on a straight-up course by angling the motor, rather like a finger balancing a 1m rod. And rather like a SpaceX Falcon 9.