Yes, in my experience personally, as well as the reports from many other trikers, 32 to 34 is about what you can expect. I have gotten as low as 28 when towing my trailer against a hard wind, will usually get closer to 30 if I persist in travelling above 70 mph, and 34 or so when I take it easier, especially around 55 mph or so. As with two wheels, every 5 mph above 55 or 60 mph reduces mpg.
I am not a hard charger. I do not normally accelerate quickly or hard. I travel most miles down the open road with my cruise set at 70 on the speedometer, which is actually about 65 or 66 mph by my gps or timed between mileposts. My average day in and day out mpg on my GL 1800 is about 32. My GL 1500 averaged about 30. Personally, I don't worry about it much. I know that I can travel up to 150 miles with no worry at all, a bit more if I need to do so, but I make it a point not to need to do so.
All of us are different, but I am not one who stresses about mpg. It is what it is. I keep strict records, just because that's what I do. I always figure annual mph, based on annual mileage and annual gallons consumed. But what it is never diminishes my pleasure in riding our trike. It just lets me know for certain when I need fuel based on the miles travelled since the last fillup. I absolutely hate to have to ride wondering if the small amount of fuel I have left will last to the next fuel stop or whether the next potential fuel stop will actually have fuel available. I have never run out of fuel while running on the top half of the tank.
I'm ready to stop and stretch every 100/150 miles anyway. If my mpg were to drop from what it normally is, then I'd be concerned. Otherwise, it's a non-issue for me. If you get 32 mpg consistently, then IMO, you are doing about what most of the rest of us trikers are doing. Go ride it and have fun!!! There will always be some who get more mpg, or at least say they do. I have no argument with them. But I have many thousands of miles experience at around 32mpg with a machine that runs very well and is in good tune. That is good enough for me!