My DS1 is in Y13 at Pate's after transferring from Cleeve (comprehensive state school) for the sixth form.
The 22 points (soon to be 57) is a standard offer that all internal DC (ie Pate's Y11) get and is the offer that is given to those external DC who have high predicted grades. Eg, in my DS's year only those external students with predicted grades of 27 points or higher from their top 8 GCSEs including maths, English and those subjects they wanted to do at A level actually received an offer. DS was predicted 4A* and 4A for his top 8 giving 28 points, which he achieved but his offer was for 22 points. Friends with lower predictions didn't get an offer. About 400 or so applied and only 100 or so got an offer.
He has really enjoyed his time there. His friends are predominantly externals with a scattering of internals. There are roughly 120 internals per year and about 80 externals in his year, so plenty to make friends with. He has really enjoyed the challenge and has done very well so far, getting 4 As at AS (no A* at AS.) He just took 4 ASs and has dropped one to take 3 at A2. Quite a few take 4 at A2 (and some take 5 ASs) but university offers are usually based on 3 A2s.
I know ASs are going to be decoupled (if that's a word) from A2 so things will be different for your DC.
The 80 externals are from a wide variety of schools. All of the Gloucester grammars, Balcarras, 10 or so from Cleeve, Bournside, CLC, Kings School in Gloucester, Dean Close, schools in Swindon and Stroud etc. The only problem has been some friends live so far away, I guess.
My DS3 is in Y9 at Cleeve and I would be happy if he wanted to try for Pate's sixth form as well.
He has had good help and advice with his UCAS form, with two of his teachers critiquing his personal statement and recommending books to read around the subject etc. They have a dedicated UCAS advisor/ administrator as nearly 100% apply to university.
Good luck! Now off to name change back!