One common source of Illusion of Transparency problems is different senses of what's a normal range. The countercharm for this is using actual numbers and not relative comparisons.

For instance, I talk to a lot of people who run conferences and meetups. Most of them anchor the size of an event off what they've seen or run. So someone might say "yeah, that was a really big convention last week!" to mean an EAG with almost two thousand people. Then someone else might say "yeah, the convention next week is looking like it's going to be a small one" and they're talking about DEF CON where twenty thousand would be a low turnout.

For another example, I like hiking. Sometimes I say I'm going on a short hiking trip, and someone reasonably assumes I'll be back in a few hours, when in fact I'm bringing a tent and three or four days of food. But I'm not that into hiking; on the trail I regularly meet people who enjoy hiking the Long Trail (~270 miles) as a short backpacking trip because it's not the Appalachian Trail! (~2,200 miles.)