You can have "dottle" left over from the very best of smokes. It isn't unusual.
As for the cake being thicker at the top and none at the bottom isn't unusual either.
However; if you maintain the cake, making it even on the sides and (IMO) thin your smokes will be more consistent.
The bottom of the bowl is the most difficult place to build a cake.
(Most of the time you will have some dottle left at the end of your smoke. Not every smoke is going to be perfect.)
Moist tobacco at the bottom could come from two different aspects of your smoke:
1) The tobacco may simply be a bit to moist.
2) The moist tobacco could be smoked to fast/hot causing steam and as the bowl progress toward the bottom the moisture content will increase, resulting in wet dottle. (Sometimes you will hear it sizzle in the bowl when you relight, and your pipe may gurgle.)
Try drying your tobacco for a bit before packing your pipe, and go slow.
Also, once your cake is established, and you have tended to it, and it has an even thickness on the sides; maintain it by screwing a paper towel into the bowl (firmly). You should do this while the bowl is still warm, for best effect.
This will do two things:
1) It will smooth the cake and maintain a consistent thickness.
2) It will remove excess moisture from the bowl and the cake.
This will allow the cake to really become solid without flaking, or excess build up, virtually eliminating the need to ream or scrape the bowl.
IMHO makes for a better smoking pipe.
Just remember; cake on the bottom of the bowl can cause the draft hole to diminish in size and can cause the pipe to become difficult to smoke. Very few of my pipes have more than just the merest coating of carbon, even after 20+ years of regular use.
Edit: Saliva isn't going to be the problem. The gurgle you may have while smoking comes from the condensation of the steam created in the bowl and collecting in the draft hole where it enters the bowl.