Does size matter?

I was in a LBS a few days helping a friend buy a new bike.
My friend was badly fitted for for his last bike (Shop sold him a 54ct Cannondale. He really needs a 50-51 based on typical formulas)
When I told the sales guy at the new store that my friend would be looking for a 50-51 effective (Seat Tube) in a compact geometry, he said size didn't matter.
With compact frames the only thing to consider is top tube length and bar height. Seat tube doesn't matter because standover height isn't an issue.
Hmmmm.
What do you think?
Dan

[Smiley]

He's correct . The effective TT length and where the handlebars sit relative to the placement of a level saddle do.

Dan - Smiley is one of Serott'a top fitters. He really knows his s*%#!

Thanks Smiley.
Hurts my head.
Let's say the guy is 5 1/2 feet tall with short legs and long torso.
He would normally ride a 50/54 standard bike.
He now decides on a compact bike. To get the same 54cm tt he needs to go with a medium size frame. Let's say that size frame has a virtual seat tube of 54cm.
His seat would be lower than most because of his short legs. Wouldn't that effect his knee/peddle position?
Dan

[Smiley]

Compact were designed for specific virtual set points . The Serotta Fierte as an example is set up for tall head set placement and shorter than square TT and seat tube as virtual . Your buddy may ride say a medium in a Specialized bike which would have say been a 54 square but most brands call out their seat tube to say top of seat collar . With short legs he should be a good candidate for a compact frame. The taller head set placement would allow your buddy to ride a negative stem rise if he's fit. Why not have your pal go to a qualified fitter and have them set up the size cycle for the geo of what ever bike brand he likes and most important is se where his KOP falls . I'd say this is most over looked aspect of fit on any bike and hard to tell untill the bike is set up on a wind trainer. Good luck and get your buddy fit first .

Good point and thanks, Smiley.
My friend bought an off the shelf Giant TCR. (Small)
He looks good on it. I will put him in a trainer today and set his correct knee position.
But only after we get back from his first 50 miler.
(-;
Dan