I'm glad Im not the only one to discover the useless self adhesive tape on the door sills. When I fitted the inner sills, they came straight back off (even when stadning on them to apply max pressure). Hopeless. I resorted to Industrial Adhesive (the sealant type) for both the inner & outers, just appying small amount mind. They are certainly stuck on now!! and most definitely mother-in-law proof. If you use this fixing method, just make sure you really want the sill covers coz they are not coming off!!!!
The outer sills do look a little short, but if you look at the second pic, you will see the door frame lip starts arching up. Even if the sill plates were longer, they could not be located any further back, only further forward towards the door hinge.