You are transferring weight to the front axles when the front height is at unhitched amount. With 1000 pounds of TW on ball only:
front axle decreased by about 400 pounds, rear axle increases by 1400 pounds.
Applying WDH such that front axle is net zero/same as unhitched. The rear axle will decrease to about +800 and 200 pounds of TW will go onto TT axles.
WD bar selection should be based on the TW. Gross trailer weight is fine for some other types when TW is closer to 10%. TTs tend to be more stable in the 13-15% range.
