With so few traders betting on a rally, it's unlikely that Federal Reserve Chairman Jerome Powell will be dovish enough at Jackson Hole today to change the dollar's fortune a great deal .
Much bigger speculative betting means he could have more influence on GBP/USD .
And GBP/USD has begun to turn higher in advance of Powell's speech.
The rise has been fuelled by hopes for some kind of Brexit solution, and hope has fuelled a big rise before.
In 2017-18, when speculators held GBP/USD shorts about the same size as today's, the hope was a no-deal exit could be avoided.
Brexit delays have hurt since then, but the GBP/USD rise in 2017-18 stretched roughly 1.25-1.45.
Given the size of those gains, those short GBP/USD have reasons to worry.
If Powell suggest more U.S. rate cuts are coming, there may be a scramble to cover positions.
GBPUSD and short positions Click here