eBay help says this about Simple Delivery postage rates for items under £100:

which I was pleased to see had a 2-10kg option at a price that was close to Yodel’s £5.21 that I use a lot. BUT… there is no option for this weight range when you select Simple Delivery for your item, it just goes from up to 2kg to up to 15kg, so making buyers pay nearly £2 more than necessary.
And why are prices cheaper if you select both Evri & RM? Makes no sense that a 1-2kg parcel is £3.71 (which will go with Evri) if you have both selected but £4.06 if you have just Evri. What is going on???