Uncle Pug once bubbled...
A too heavy weight belt with offsetting gas in your wing will put you in the typical rototiller position: head up body inclined at a 45 degree angle.
This will direct the force of your finning down destroying the viz... but worse yet it will cause you to plan upward and this must be countered by more weight on the belt.
When you stop finning and the upward planning effect ceases you will begin to sink. This is why rototillers are constantly finning.
Not only will correct weighting allow your to control your ascent but it will also allow you to remain motionless while maintaining depth.
If the correct weight to get diver A down is 20 lbs and diver A puts an extra 2 lbs of weight on, he/she is overweighted 10%, in terms of total weight required, which is not a big deal IMO. It certainly does not, IME, automatically mean diver A will be swimming at a 45 and sinking when swimming stops. Breath control has more effect on buoyancy in this case.
Now if diver B only needs 10 lbs to be correctly weighted and diver B adds the same 2 lbs, now he /she in overweighted by 20% or double diver A. Diver B will be much more prone to have problems like your describing above than diver A for that reason.
I guess my point is, there is a huge difference between being slightly overweighted and grossly overweighted. For the same reason you like to do a 5 FPM ascent from 5 feet, i like to see newer divers slightly overweighted .... 10 to 20%. That way they are less prone to ascend rapidly and miss a good slow ascent and safety stop.
Once a diver is confident they won't ever miss a safety stop or will always perform a good, slow ascent, i say go for it and weight yourself to the grain if your that confident. Lets see .... 7000 grains per lb gives one mucho room for fine tuning.
IME, weighting requirements for most divers can easily vary +/- 10% or more, due to things like mental state, water temp & conditions, physical state, etc.
JMO
