Whether the troop is using the patrol method or not I don't think has so much to do with the troop size as it has to do with the Scoutmaster and the Troop Committee and how dedicated they are to letting the boys lead.
Bigger troops tend to have bigger programs, more money for equipment, etc. These are things that can be readily seen when you go camping with them.
Smaller troops may also have advantages, but those advantages are less tangible and no guarantee.
I would recommend you ask questions about things that may have impact years down the road. For example, what is the troop's relation to the Chartering Organization? Does the CO really oversee and support the troop or are they just the CO on paper? Does the CO Rep actually meet with the Troop Committee? Was the Troop Committee actually selected by the CO or is it just a small group of parents learning the job as they go and possibly bogged down with a lot of disagreements because they have no unifying vision?
How was the Scoutmaster chosen by the Troop Committee? Was there a careful selection process, or was he just the only dad who was willing to do the job for a couple years, but only until his son makes Eagle? How likely then is it that the vision of the troop will change drastically when the the next parent Scoutmaster takes over?
These are important questions that I wish I'd asked when my son got into Scouting, but I had no clue.
Good luck.