confusion over DIP/criteria on intermediaries site and chances of mortgage

Hi, I'm somewhat confused and hope someone with more knowledge and experience than me can help? ( so that's pretty much anyone! )

My son is looking to buy his first home, and as such applied online for a DIP, which he got, from HSBC, he earns £27 200 p.a and the DIP came back at £129200...4,75x his salary, incidentally the Halifax 'how much can I borrow?' calculator came out at same figure but he did the HSBC DIP as it had more favourable rates.

He's been looking at houses priced 110-120 000, so well within his range (including his 10% deposit), but nothing has been of an ok standard, However, a more expensive house has come up that seems of a good standard and that, IF, he were able to get the maximum lending amount he could afford by putting in slightly over 10% deposit.

Obviously I'm not overly confident of achieving the highest lending amount so have been trying to research the lenders criteria.

On the HSBC intermediaries site it states:
4.49 times income for applications with income of less than £30k
4.75 times income for applications with income of £30k or more

which leads me to ask why he was given a DIP equalling 4.75x when he clearly should have been in the 4.49 bracket?

Curiously enough, the Halifax intermediaries site states :
INCOME - £25K-£75K
LTV: LOANS <=£500K:
0-75% - 4.75x (5.00x if income >=£50K)
75.01 - 90% - 4.75x
90.01 - 95% - 4.49x

As he would have an LTV of slightly under 90% it appears as though he MIGHT actually qualify via Halifax?

He has no debt other than student loan which is being paid back at £11 a month, no car/finance/loans.

He pays £91 (4%) to his pension every month and puts £8 (netflix) on his only credit card every month and pays it off just so he can leave a 'credit footprint'. he has no social life (and even less interest in having one!), doesn't drink or smoke, no travel costs as he walks to/from work and doesn't go anywhere else ( he's a very dull boy indeed, at least by 24 year old standards lol)

Does he seem to stand any chance of achieving the 4.75x from Halifax? as if not a chance I wouldn't want to get his hopes up for this more expensive house, and would keep him looking at more affordable options.

Oh, the house he's looking at is leasehold but has 737 years remaining with a ground rent of £8 p.a, if that affects anything? (when we did the intermediary calculator the difference from putting freehold to leasehold reduced the maximum loan amount at a term of 25 years but upped it back to 4.75x if the term was 30 years)

Thank you for taking the time to read this and for any help/advice/experience you are able to give.