Hi NF_Diver,
Our wonderful Jessica is on maternity leave. I read your post and asked Dave Sweetin for some help on responding to your question. If you don't know Dave Sweetin he handles our DOG Rally & Demo Tour and he is also a long time diver and big into tech diving.
Here are some suggestions from Dave:
It sounds as though the Delta is out of adjustment. This is quite common given the amount of adjustability it has built in the design. I'd recommend tweaking the sizing a bit over a few dives to find the proper position. Tighten the crotch and waist straps, once the shoulder straps are adjusted properly to support without a lot of slop thus preventing that "sinking down into your BC while floating at the surface issue". You've seen it at the dive site...the diver looking back to the boat through the arm hole of their ill fitted BC.
Take note of how moving the BC up or down on the cylinder effects the diver trim position when horizontal in the water. The position of the tank is the foundation and it can only be so far away from a diver. The length of the inflator hose is also fixed (and in my opinion too long, but that's the tech diver in me). Therefore if the inflator hose is waaaay up on your shoulder it would seem that the tank is riding very low and or there is a lot of slop in the adjustment of the straps.
Concerning the "pushing forward" - This is a common symptom of a back inflated BC with straps out of adjustment. We deal with this everyday when divers are transitioning to Tech or Cave diving. That is to say, the BC air cell (behind you) will always seek to float flat at the surface. If the crotch strap and waist strap are loose along with the shoulder straps, it gives the BC air cell room to move away from the diver's back and try to float flat on the surface of the water. In so doing it is trying to push the diver over and face down into the water, and that just sucks.
However, if a diver has the proper tension on the waist strap and crotch strap and fitted shoulder straps, the tank and BC air cell move with him. There is no room for the air cell to move away from the diver's body and it has to move with the diver. It eliminates the "sinking into your BC at the surface" issue. Now all one has to do when resting at the surface is lean back comfortably. Your knees will naturally bend slightly and find a comfortable resting position.
It is the hardest trick in SCUBA; to be comfortable and aware enough to get in the water or underwater to simply do nothing - Rest at ease (stop kicking for no reason) and not have to fight and fidget to stay there.
This is balance. It is a result of many dives, proper trim, and neutral buoyancy...you know, the "Holy Grail" of diving.
Thanks, that was fun.
Dave
One last comment. If you are near a DOG Rally & Demo Tour and can bring your Delta to the event our DOG Rally Crew - and Dave will be there as well - is ready to assit you.