The location and shape of the Tummy Tuck (Abdominoplasty) scar in my opinion should be TOTALLY up to you. But - you need to understand what your choice would mean.
If your read between the lines (no pun intended...), there are several preferences for Tummy Tuck scars among Plastic surgeons.
The Geometrical approach - pick the belly button as the apex of a triangle - and base the height of the side scars on the length of an imaginary triangle with equal limbs - resulting in higher arching scars sideways.
The Customized Tailoring approach - The surgeon picks the transverse location of the scar based on your preferred style of underwear / lower bathing suit which YOU plan on wearing from now on. You decide how low the scar will be - we work with that as the limiting factor.
The advantage of doing it this way is the transverse scar is hidden even with low underwear. The disadvantage is than in women with NOT a lot of excess lower tummy skin, the former location of the belly button cannot be removed and results in a short vertical scar, often hidden by your clothes.
I prefer to let my patient choose the location of their scar. It empowers them, and they become an important part of the decision.
Summary - You SHOULD be able to pick the scar YOU WANT - not accept a scar you do not want.