Have you tried different dosing techniques?* Try using a toothpick to stir the grinds up before you tamp and see if it makes a difference (see Weiss Distribution Technique or WDT).* Some people are horrified with this, but they obviously dont have a grinder that clumps or dumps on one side. (thats another point - make sure the dose is coming out evenly).
Theres another one I use but I cant remember what its called - a style of grooming.* It can be done in conjunction with the WDT or alone.* Use your first one or two fingers to "mould" the coffee in each part of the basket, clockwise and anticlockwise.* Dont stick your fingers in, but hold them almost flat over the top and rotate your hand around.* That doesnt really make sense but I cant remember what its called so I cant look it up.* Ive seen a few different ways of doing this so dont know what works best.* The idea is to evenly push the grinds into the corners of the basket.
I dont have a naked pf for my Giotto, but I did use one on the Breville.* The above two techniques drastically improved my naked pours.* Most of the time* ::)
Hope that helps a bit - Im no expert on Giottos nor HXs in general, having only had one for a month or so :)
(edit) sounds like youre dosing a bit high also - I was surprised at how small the correct dose looked when I first got it right!