If when you do a reg. cleaning and as the heads move off the captops, is it pooling in the captop and then slowly drains? What might be happening is that the head is flooded with ink on the bottom and then when it wipes the wiper is so full it sprays the inks off as it flips back from wiping the heads.
Drain lines can be partialy plugged or the clear lines under the captops are plugged and not clear all the way over to that rectangle box on the right.
You should only get a nice thin band of ink off the heads on the wiper which may still spray a bit but not like it does when the heads are sitting in ink.
I tend to clean the wiper after every cleaning on startup or general cleanings so that I don't get a sludge of ink build up. I also keep the front cover off of that area so that I can see this happening.