Mobile networking specialist Richard Gaywood, who spotted the iPhone 4’s lopsided signal-mapping formula even before Apple (AAPL) owned up to it Friday, has used data from Anandtech’s similar analysis to diagram the problem. Here’s his explanation — and his diagram:

“The mapping of signal strength to reported ‘bars’ on the iPhone’s display is oddly out of whack, which causes two problems. For users already in a marginal signal strength area, it makes the drop in reception when they hold the phone look disproportionately — and alarmingly — worse (as the phone can drop from five bars to none). For users in a strong signal area, it masks the issue completely (as the phone’s reception is still inside the five bar range). These are the two positions we’ve seen rage in discussion forums across the Internet over the last eight days (“it sucks!” / “no, it’s fine, you suck!”, etc etc). Basically, it looks like this:”

Apple’s position is that the antenna on the iPhone 4 is so good that even when the signal is attenuated, the reception still better than any previous iPhone.

“They, of course, would say that; they’ve just sold a couple of million of the things,” writes Gaywood. “Maybe they’re right but I remain unconvinced.”

For Gaywood’s full explanation, click here.

See also:

• Death Grip: Apple blames the bars
• How bad is the iPhone 4’s signal loss?
• The iPhone 4 Death Grip saga

[Follow Philip Elmer-DeWitt on Twitter @philiped]