Low lying placenta question 🙋

Hi I was re-scanned last week (at 34 weeks)  to check what my placenta was up to (because at 20 weeks it was 'close' to internal os.)

This time sonographer says it's not really moved and is still only 6mm away and is posterior. Apparently the hospital policy states that a posterior placenta should be 4cms from internal os for them to consider it to be a safe option to deliver vaginally. Im to go back for re-scan at 38 weeks then see consultant straight after. 

My question is,  has anyone been through similar and if so did your placenta move sufficiently in just 4 weeks for a vaginal delivery to be an option?  And if so, were there any associated problems?

Thank you in advance 😊 xx