Hi Clint
Your method is a fly sparge and you're doing it the preferred way by keeping the water level above the grain. The all-in-one systems like the GF also use a fly sparge, but the difference is you can't control the outlet, it'll drain as fast as the grain bed allows. So in theory this will be less efficient than your method.
... I agree with what Steve's said there, but you need to recognise that that's only comparing the efficiency drop caused by sparging (the reduction from post-mash efficiency to the pre-boil efficiency) ... the recirculating mash of all-in-one systems will tend to increase mash-effiiciency, and on occasions it will more than compensate for the less efficient sparging in those systems when compared with fly-sparged mash-tuns.
In many ways, comparing efficiencies with other brewers using other systems (or even using the same/similar system) is about as useful as seeing who can wee highest up a wall
... so rather than investigating whether you can improve your efficiencies because other people are reporting bigger numbers (if that's a worry you could just go into your chosen brewing calculator and reduce the extract potential of the grains you use in recipes and you'll get bigger numbers for efficiency for brews you do with those grains, in future
) ... I'd suggest you only put effort into investigating improving efficiencies if you feel you're not getting good enough efficiency from your methods and you're not happy to just use a bit more grain to compensate.
Have you tried batch sparging? It's supposedly less efficient than fly sparging, but when I was 3V brewing with a picnic cooler I actually found batch sparging increased my efficiency a little.
... and I'm pretty sure I've seen other home-brewers find that also ... that "theory" that fly-sparging is more efficient than batch-sparging is dependent on operating a slow, steady flow of water into the top of the grain bed and a similar rate of flow of wort lautered from the bottom, and with all due respect, managing that precisely when jugging water isn't always that manageable ... two or three batch sparges can be performed in similar timescales to a slow, steady fly-sparge, and can be more efficient than a "quickly or poorly" performed fly-sparge
Cheers, PhilB