I've got a massive head and the largest previous model of Masuri's just didn't fit and felt like it was just balancing on top of my head. Has anyone who may have suffered similar issues tried the new model, is it any different?
I've had similar issues. When measured, it's clear that the circumference of my head's not unusually large. But I had the same experience as you. Helmets that just balanced on top. For me, it's shape rather than overall size. I think mine's slightly longer, front to back, than most homo sapiens, or maybe a bit deeper (though no one has ever remarked on it). In the past, motorbike helmets were always problematic.
I tried on every batting helmet going, and eventually settled on an Ayrtek with the ACIS. Even that, though, wasn't ideal, as the grill sat quite high on my chin.
I was really keen to try the new Masuri Senior Large, but couldn't find any shop that had one in stock, so I went to their nearby HQ in December and tried one on. The good news was that it works for me. It's the best fit I've found. If I was to quibble, it sits fractionally low on my forehead, so I might put in some strategically placed foam for the perfect fit. It also has an adjustable bit at the back. Better to have a helmet that's slightly too large, that can be adjusted to fit, than one that you can't even force on.
I recommend you try one.