That's right weight in air is meaningless, get your self a luggage scale and weigh it in water, fresh water is close enough - make it slightly negative, a positive housing is a pain to use. What's the big dome/lens - WWL?
As far as the best system goes any of the float systems will work, the float arms don't compress which is a plus, but they are pricier. The INON arms and the Nauticam arms are both good, BUT you need the right size and the only way to find that out is to weigh the system in water. Then each arm has a buoyancy in the specs . Once you know how much it weighs in water you can then work out how many of which model float arm are needed to cancel out that weight. Here's the specs for the INON arms:
INON Arm System [Arm] click on the float arm to jump to the specs.
For example if you weighed the rig and it weighed 850grams underwater then two "INON mega float arms S" at -390gram each would provide -780 grams buoyancy which is probably about right and the rig would only weigh 70 gr underwater which is close enough. Unless you have an adjustable system you can only get in the ballpark for neutral buoyancy for your rig. Remember you are constrained by balancing the rig so you need two arms minimum.
It looks like you have two Float arm S which are -75 gram each for a total of -150gr, which is not much so not surprised it doesn't seem to have much effect.
You can use two float arms each side or a single which ever matches best and also take into account if to use need a float collar for the big lens - if it's a WWL it is quite heavy in water.
Also when you weigh it in water leave out the float arms unless you are planning to use them along with another arm each side.
