Medium to Large Speed Concept Help

(First a side note: I just came back to this site on a lark, after years away.  I have to say, it is much much slower than it was.  I'm too busy to post more than once in a blue moon, but here goes.)

1.  If you have good reason to trust the fitter, then go with it for now; give yourself time to get used to it.  If you cannot get used to it (after, say, 200 miles in the saddle), then something is probably wrong -- could be simply too extreme of an aero position for your flexibility and experience, or a bad fit generally (either due to the fitter or due to the fact that you just don't fit on the bike).

2.  If you've never been on a tri bike before then yes, you will feel a bit awkward and 'forward'.

3.  If the bike is too small, this feeling will be exacerbated.

4.  There's not a lot that you can do, past a certain point, if the bike is too small.  You will feel cramped on it and you will not have full power and you will be sorely tempted to sit up.  (You would probably be sorely tempted to sit up when you are first learning to ride in the aero position in any case, so at first it is going to be hard to distinguish 'bad fit' from 'learning aero.')

If the bike really is too small for you, then you'd really be best off selling it and getting a larger one.  That's a painful prospect, I'm sure, but not nearly as painful as a bad fit over months and years of training and racing.

When you got your fit, did you get stack and reach numbers?  A good fitter would have given you those numbers.

If you have stack/reach you can look at the geometry of the SC and see where your numbers line up.

IF - and that  can be a VERY big if - your fitter is a good fitter, him/her saying you were pretty close would be somewhat comforting.  If you didn't pay at least a couple hundred dollars or more for you fit session then you may have gotten what you paid for.

Next step - ride the bike, going to a TT bike, even a perfectly fit TT bike from a road bike is going to feel awkward.  Put some miles on it and get past that initial awkwardness.  If you have stack/reach post those numbers.  Maybe post a picture of you on the bike.  There are some pretty knowledgeable people here that can look at a picture and offer an opinion on how your fit is.  Mind you, that isn't a replacement for a proper fit, but if your bike is way too small, it will likely be obvious in a picture.