Let me add a little bit more.
Am 1,72 and also an F800ST owner (and my missus is shorter too), there my problems were solved with the extra low seat, uncomfortable for commuting outside the city but perfect for in the city runs.
The optional low seat in the big K took 2,5 cm from the height.
Another 2,5 were taken with the purchase of the lowering set fm HORNIG that combination transformed the bike and allows both feet stepping steady on the ground, now pillions can climb much easier, add the agility of the bike to exit curves at higher speed being lower.
The other issue with the handle bars was solved with the use of new IDE bars , that removed bars towards me 3,5 cm and raised them by 3 cm.
The option for the low seat (like mine) took another 2,5 cm from the height.
Another significant change was made to the pegs , by getting the HP sets I'm now able to change and try every possible position of them and finally was able to find the perfect set up for me.
Finally the thick tank grips bought, enabled me to really feel the tank under my feet and grip on it for hitting curves better.
About the seat IMHO no seat whatever seat you try (Sargent, Corbin, seat cushions, seat grip pads etc) will ever stop your pillion to push you forward, its a long seat that is the issue. Solutions like the handle bar grips for pillion, the love belt and others were also used without success. My pillions are instructed to keep pressure in their pegs especially during braking and whenever possible keep both hands on pillion bars. I've even consider changing the missus with a new higher model but that didn't work.....