The reason why the short needles are recommended is simply because somebody (can't remember which Uni Med School it was now, it's been a while) actually went to the trouble of measuring all sorts of people's skin thickness, all ages, men women kids, sedentary, athletic, manual workers, librarians - people who lavish their bodies with creams frequently - people that didn't LOL - to get to the bit where the insulin needs to go - under the epidermis, in the space where the interstitial fluid flows between it and the fat and tissue below that. And the answer was around 4mm.
I found em a tad short TBH - and I've never got on with BD needles - they sting me - so I went with 6mm - Novofine ones in my case cos they don't make 5mm ones. I only had to ask and I got. They are still specified on my 'repeat' prescription.
When CCGs issue edicts like everyone must use this meter for which the strips are cheaper - and in any case can only have 100 each month - every GP in the land has a code he can enter in his computer to override the automatic choice of the computer program. Depending on what item he's actually prescribing he then gets a list of 'tick box' probably choices for his reason - or he can type his own reason freehand. I mean I'm using a pump and so they tick that as the 'excuse' - it isn't true, I still needed more on MDI anyway but I had a history of being a bit uncontrolled in the near past at the time, so they said it was cos I'd been advised by the hospital to test more. I couldn't care less if they said it was cos I was an ugly old woman and stroppy - as long as I got the ruddy things!
You do really need to get a GP with more than one brain cell - but meanwhile - you really should try to help yourself - cos it's amazing - the NHS engage far far better, with people who try and help themselves and can demonstrate that they do.
First thing you need to do is some basal testing, to make sure your dose of Tresiba is doing what it should for you. If not - then it needs adjusting up or down. So here it is -
http://www.diabetes-support.org.uk/info/?page_id=120 Keep a record of what happens - and then work out either yourself or with our help on here - how you can try and overcome any glitches.
Good luck !