Back again...I've noticed one thing over the last year - Instead of listing a package with the actual dimensions if they are exactly at a particular inch measurement I now round up. In other words if a dimension is for example RIGHT AT 10" I'll just say it's 11" as if it was 10 1/2 to start with. I assume it's a scanning device on a conveyor belt somehow measuring the packages instead of a live person doing it manually and believe that it perhaps measures even if one corner is bulging slightly or something like that.
Anyway, doing this has VASTLY reduced my number of "adjustments" with FedEx and UPS. USPS doesn't seem to care, they in fact sometimes give me money BACK for whatever reason.
In other words if a package actually measures at 10x10x10 I'll treat it as if it measured 10.25x10.25x10.25 and just call it an 11x11x11. The "adjustment" rate appears to include a penalty, not just the actual rate difference, so not worth the risk or hassle (to me anyway).
