Actually the frame register came out of the Law Enforcement field in the mid 80's. If memory serves me right I think it was Emanuel Kaphelsohn defending an officer in an accidental shooting who first brought to fore the involuntary physiological issues that OrigamiAK mentioned. It was then researched by many instructors and found to be valid.
In 25 years I have yet to find anyone whose hand was to small to achieve a solid frame register. For those who use their trigger finger to release the magazine either with the traditional button or the non traditional paddle, there is no reason after the magazine is released for the finger not to immediately assume a frame register.
Leroy if you can actually "wrap" your finger around the front of the trigger guard I see no issues with that. A lot of people don't have long enough fingers to achieve the wrap. If you are just getting the pad of the trigger finger on the side of the trigger guard that is an issue. In testing fingers registered on the side of the trigger guard were more likely to slip and engage the trigger under the conditions that triggered the physiological responses mentioned earlier.
When I SO if your finger is outside the trigger when required even if it is not registered on the frame you are golden. I will mention/suggest to the shooter at Club matches that a frame register will be safer in the most likely event that would cause a finger to involuntary migrate to the trigger, that being loss of balance/tripping.