How did that person get an 11" penis through phalloplasty with no complications? My sincere guess would be that they didn't, and that they are a liar.
When you're talking to people about bottom surgery experiences, only talk to people who are 100% transparent. So many guys downplay their complications when they talk about their experiences online. I think the rate of complications that surgeons speak about is accurate, but I don't think online experiences (especially from a single person) are a good basis for judging what your own medical experience would be.
To answer your topic question - this will be entirely dependent on your body, and the surgeon you choose. If being big is important to you, you will need to be very up front with the surgeon you consult with and let them know that you do not want anything smaller than X". You will likely get some pushback for good reason.
If you want to increase your chances of being larger than average, I would suggest extensive research into ALT phalloplasty. ALT is recommended for thinner guys with a low body fat percentage. It uses tissue from the thigh to create the phallus. As that area of the body tends to be fattier even in an ideal patient, it generally results in a very girthy phallus post-op. It can be de-girthed at a second or third stage if necessary.
I would also suggest taking it one day at a time. You haven't even started to medically transition yet. Most surgeons will not discuss phalloplasty with you until you've been on T for a year (unless there is a medical reason why you cannot be on T), have legally been living as male for a year, and have had other secondary GRS procedures done like top surgery or a hysterectomy. I definitely understand wanting to know what your options are, but realistically you're looking at ~2 years between now and the soonest you'd be able to get this done. Techniques could change by then. They may find ways to increase circulation in the neophallus that would safely allow for larger ones to be created.
