I tried the simple route first ( while I read through that novel length thread for behind the neck rest mounting). I'll try this water bottle position and if it works OK then I'm good. If not, or if I do a super long ride like STP...I probably will order the topeak seat mounts and use inner tube to fine tune. The mesh neck rest cover seems to interfere with that attachment method, but I suppose I could cut access slots or just scoot the mesh up in back?
As a designer, I can see several "detail issues" with the vendetta which will likely get resolved with further evolution and rider input. The design is very new compared to DF bikes that have undergone decades of working out the details. The lip of the seat interfering with the mounting of water bottle cages is a minor thing, but access to water is a major thing. There is likely a reason for the flared seat lip that escapes me.