You will find this is the same with most people, and more with some.

However, you are almost certainly going to be faster.

My N=1 is about 20 watts (FTP 260), yet I am averaging 1.5mph+ more on the TT bike (AVG 23.1 on last HIM @ 195 watts)

Don't worry about it, as long as you are faster overall.

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On the internet, you can be anything you want. It is a pity so many people choose to be stupid.

Did you perform your 20' power on the road on each bike or on the turbo?
How often are you on your tri bike?
Spend more time on the tri bike will likely yield closer wattage as you may not feel as comfortable maintaining position. Aero without being comfortable often yields unfavorable results.
Most find it a little more difficult to maintain same wattage on tri/TT bike vs road because of the reduced aerodynamic drag.
As stated from the previous post, you are still likely faster on the tri bike even though less power.

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My YouTube channel- https://www.youtube.com/ksquaredcycling
Time RXR Super Record | Cipollini Bond Campgnolo EPS | Specialized Shiv TT SWorks Super Record | Colnago C59 SR-EPS | Colnago EPS Super Record | Colnago Prestige Ui2

Drop the saddle 5-10 mm, drop the cockpit an equivalent amount, and if you race long course, consider shorter cranks (your hips are very closed at the top of the pedal stroke).

When a rider's saddle is too high, I frequently see a drop in the ability to push power at the bottom of the pedal stroke. As others have said, you should expect to drive less power in the tri/TT position.

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Trent Nix
Owned and operated Tri Shop
F.I.S.T. Advanced Certified Fitter | Retul Master Certified Fitter (back when those were things)