if it comes out anny you are shifting the plane to anhyzer, most likely caused by your elbow not stopping and/or having your elbow above the disc while attempting a flat throw.
wrist extension and sound grip fundamentals are really what give nose down. the other major fundamentals don't GIVE nose down, but lacking them force nose up. make sense?
ideal fundamentals that will help get the nose down:
-disc parallel to forearm. what this really does is line up the hinge of the wrist joint with the plane of the elbow joint = the uncoiling of the elbow and uncoiling of the wrist provide force parallel to the disc plane = greatest potential power that is on axis.
-keeping the disc close during the pull = allows for the wrist to extend with the disc moving in the forwards direction. if the disc is wide during the pull the wrist will not extend unless it is a grip lock. nose down can be achieved here but only with anhyzers or grip locks.
-getting weight forward = allows your shoulders/arm to continue rotating on plane. weight back jams the pivot and forces the wrist to roll under late in the power zone if you try to keep your shoulders/arm on plane = nose up. this can be compensated for by breaking the shoulder plane in an OAT over motion but adds a SIGNIFICANT amount of OAT. as always, jamming the pivot puts tremendous strain on the ACL/MCL/LCL and patellar tendon if you attempt a complete follow through (or risk of shoulder damage if you break the lower body follow through off).
it is possible in extreme cases to "power through" and force the nose down even without having the above fundamentals. this requires being able to generate 60+mph worth of disc velocity without having the above fundamentals happening. i've maybe come across 2 people ever who could do this out of everyone i've seen throw.
to summarize: certain positions facilitate the required motion for nose down (about 1" of wrist extension at the right time). failing to achieve those positions will block that from happening unless you have freakish natural ability.
Where is the apex of the throw, and does the disc glide "downhill" from the apex at an angle, or does it just sort of lose altitude as it runs out of steam like a putter?
this is completely dependent upon your throwing velocity, nose down, and the disc selection. you are best off working with incredibly slow plastic if you want to see what is supposed to happen.