Thanks. I've been able to compare your figures with mine and I've examined it some more. I've determined that it boils down to the top back edge of the cowl tapering downward when the cowl is stretching a bit around the nose. If the battery hatch is installed before putting on the cowl, then it squeazes that down like a vice. When the hatch is left off, the downward taper gets in the way of allowing it to slip foward enough for the back section of the hatch to start slipping down and forward on to it's seat.

So it's just a minor variation in the form of my cowl.

I've been marking with a pen on the cowl where exactly the sticking points are. I figure that I could just use a fine grinding stone drill bit to carve out a sort of "moon sliver" on the back top edge of the cowl. Unless looking at it closely, it should be hardly noticable.

So looks like it will be ok and requiring no radical modification.

Thanks for your help