The one gallon mark on those jugs is just above where it starts to narrow. Its more like 1.25 total. A blow off tube is a necessary item for these batches but if you have precise temp control you don't always get any blow off. Once you break the 8% ABV range, your more than likely to get some. I just did a barleywine and even at 58 degrees, I lost some.
Even worse though is when the krausen comes to the top and dries there, you have to break through with your siphon and really damages clarity...its one of the reasons I usually secondary with my 1 gallon brews