I had the same problem with my old pulsoids and again with my new x-10s which haven't even seen a bottle through them yet, is it likely they were both blocked?
It is extremely unlikely that both had blocked filters, however;
1) If you had a bad fill that put a substantial amount of crap in to your bottle and
2) Both sets of Pulsoids we used while that crap was being disposed of through the system,
It is possible for both filters to get blocked.
I've just serviced a set of Pulsoids for another customer and the amount of crap that was in the filter was ASTONISHING!!!!Is it essential to run the nos filter or can it be removed for more flow?
Under normal conditions (when the gas isn't suspect of being full of crap), it isn't 'essential' to have a filter but I certainly wouldn't advise leaving it out permanently. I only suggested it as a last ditch effort to locate the problem and I'm in 2 minds about doing so, as it's possible you still have crap in the system and removing the filter would allow it to get in to the Pulsoid, which could lead to MAJOR problems.
If you decide to remove the filter, be ready to cut the ignition if the Pulsoid didn't shut due to crap.
What method do you have of activating the system, are you using the TPS feature in the Max or a throttle switch?
If you're using the TPS feature, what setting do you have it set to? Car only smoked on launch at drag days, unfortunately my local airfield doesn't have any recent events and the next meet is next march. I haven't launched it on the road as I would on the strip for obvious reasons, if required I will do this under controlled conditions when visiting WON next month for test purposes. However coolant level has stayed consistant so far.
A hard launch shouldn't be a problem on the road, especially if the nitrous is under performing, so I'd give that a shot ASAP if I were you but otherwise we can do that when you're here.
IF it no longer smokes under ANY circumstances, the cause of the problem was the head bolts 'stretching' and allowing water in to the combustion chamber and IF that was the case, it's a surprise that you haven't experienced at least some improvement to your performance since improving the components.Maybe it all works fine but my heavier than most hatchback (1240kg) is too big to tug along and make a difference. Maybe you could test my car for suitability for upping to a 75bhp shot ( dare I suggest it ).
There is always the possibility that your particular engine won't respond correctly until it reaches a higher level of nitrous. We have seen that be the case a couple of times and most engines do have a 'sweet spot' where a given amount of nitrous produces the best results, when more or less doesn't produce such impressive results, but the results up to that level are usually still acceptable, which in your case they seem not to be.
It's certainly looking like 'we/I' need to see your car to solve this one and given that opportunity we WILL solve it. 
Then activate the nitrous pulsoid for 5 seconds and weigh the bottle again. if the drop in weight is correct for the jetting you have... THEN you can look at re jetting for less fuel.